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How to generate a self-signed SSL certificate using OpenSSL?

I'm adding HTTPS support to an embedded Linux device. I have tried to generate a self-signed certificate with these steps:

openssl req -new > cert.csr
openssl rsa -in privkey.pem -out key.pem
openssl x509 -in cert.csr -out cert.pem -req -signkey key.pem -days 1001
cat key.pem>>cert.pem

This works, but I get some errors with, for example, Google Chrome:

This is probably not the site you are looking for! The site's security certificate is not trusted!

Am I missing something? Is this the correct way to build a self-signed certificate?

Self-signed certificates are considered insecure for the Internet. Firefox will treat the site as having an invalid certificate, while Chrome will act as if the connection was plain HTTP. More details: gerv.net/security/self-signed-certs
You need to import your CA certificate into your browsers and tell the browsers you trust the certificate -or- get it signed by one of the big money-for-nothing organizations that are already trusted by the browsers -or- ignore the warning and click past it. I like the last option myself.
You should not use the "stock" OpenSSL settings like that. That's because you cannot place DNS names in the Subject Alternate Name (SAN). You need to provide a configuration file with an alternate_names section and pass it with the -config option. Also, placing a DNS name in the Common Name (CN) is deprecated (but not prohibited) by both the IETF and the CA/Browser Forums. Any DNS name in the CN must also be present in the SAN. There's no way to avoid using the SAN. See answer below.
In addition to @jww 's comment. Per may 2017 Chrome doesn't accept certs w/o (emtpy) SAN's anymore: "The certificate for this site does not contain a Subject Alternative Name extension containing a domain name or IP address."
These days, as long as your webserver is accessible by its FQDN on port 80 over the internet, you can use LetsEncrypt and get free full CA certs (valid for 90 days, renewal can be automated) that won't give any browser warnings/messages. www.letsencrypt.com

M
Mark Amery

You can do that in one command:

openssl req -x509 -newkey rsa:4096 -keyout key.pem -out cert.pem -sha256 -days 365

You can also add -nodes (short for "no DES") if you don't want to protect your private key with a passphrase. Otherwise it will prompt you for "at least a 4 character" password.

The days parameter (365) you can replace with any number to affect the expiration date. It will then prompt you for things like "Country Name", but you can just hit Enter and accept the defaults.

Add -subj '/CN=localhost' to suppress questions about the contents of the certificate (replace localhost with your desired domain).

Self-signed certificates are not validated with any third party unless you import them to the browsers previously. If you need more security, you should use a certificate signed by a certificate authority (CA).


For anyone who's interested, here is the documentation, if you want to verify anything yourself.
How does signing with a 3rd-party provide more security?
For anyone else using this in automation, here's all of the common parameters for the subject: -subj "/C=US/ST=Oregon/L=Portland/O=Company Name/OU=Org/CN=www.example.com"
@JamesMills I mean, think about it -- if a shady looking guy with "free candy" written on the side of his van invites you to come inside, you're totally going to think twice and be on guard about it -- but if someone you trust -- like really trust -- is all like, "naw man, he's legit" you're going to be all about that free candy.
Remember to use -sha256 to generate SHA-256-based certificate.
C
Community

Am I missing something? Is this the correct way to build a self-signed certificate?

It's easy to create a self-signed certificate. You just use the openssl req command. It can be tricky to create one that can be consumed by the largest selection of clients, like browsers and command line tools.

It's difficult because the browsers have their own set of requirements, and they are more restrictive than the IETF. The requirements used by browsers are documented at the CA/Browser Forums (see references below). The restrictions arise in two key areas: (1) trust anchors, and (2) DNS names.

Modern browsers (like the warez we're using in 2014/2015) want a certificate that chains back to a trust anchor, and they want DNS names to be presented in particular ways in the certificate. And browsers are actively moving against self-signed server certificates.

Some browsers don't exactly make it easy to import a self-signed server certificate. In fact, you can't with some browsers, like Android's browser. So the complete solution is to become your own authority.

In the absence of becoming your own authority, you have to get the DNS names right to give the certificate the greatest chance of success. But I would encourage you to become your own authority. It's easy to become your own authority, and it will sidestep all the trust issues (who better to trust than yourself?).

This is probably not the site you are looking for! The site's security certificate is not trusted!

This is because browsers use a predefined list of trust anchors to validate server certificates. A self-signed certificate does not chain back to a trusted anchor.

The best way to avoid this is:

Create your own authority (i.e., become a CA) Create a certificate signing request (CSR) for the server Sign the server's CSR with your CA key Install the server certificate on the server Install the CA certificate on the client

Step 1 - Create your own authority just means to create a self-signed certificate with CA: true and proper key usage. That means the Subject and Issuer are the same entity, CA is set to true in Basic Constraints (it should also be marked as critical), key usage is keyCertSign and crlSign (if you are using CRLs), and the Subject Key Identifier (SKI) is the same as the Authority Key Identifier (AKI).

To become your own certificate authority, see *How do you sign a certificate signing request with your certification authority? on Stack Overflow. Then, import your CA into the Trust Store used by the browser.

Steps 2 - 4 are roughly what you do now for a public facing server when you enlist the services of a CA like Startcom or CAcert. Steps 1 and 5 allows you to avoid the third-party authority, and act as your own authority (who better to trust than yourself?).

The next best way to avoid the browser warning is to trust the server's certificate. But some browsers, like Android's default browser, do not let you do it. So it will never work on the platform.

The issue of browsers (and other similar user agents) not trusting self-signed certificates is going to be a big problem in the Internet of Things (IoT). For example, what is going to happen when you connect to your thermostat or refrigerator to program it? The answer is, nothing good as far as the user experience is concerned.

The W3C's WebAppSec Working Group is starting to look at the issue. See, for example, Proposal: Marking HTTP As Non-Secure.

How to create a self-signed certificate with OpenSSL

The commands below and the configuration file create a self-signed certificate (it also shows you how to create a signing request). They differ from other answers in one respect: the DNS names used for the self signed certificate are in the Subject Alternate Name (SAN), and not the Common Name (CN).

The DNS names are placed in the SAN through the configuration file with the line subjectAltName = @alternate_names (there's no way to do it through the command line). Then there's an alternate_names section in the configuration file (you should tune this to suit your taste):

[ alternate_names ]

DNS.1       = example.com
DNS.2       = www.example.com
DNS.3       = mail.example.com
DNS.4       = ftp.example.com

# Add these if you need them. But usually you don't want them or
#   need them in production. You may need them for development.
# DNS.5       = localhost
# DNS.6       = localhost.localdomain
# IP.1        = 127.0.0.1
# IP.2        = ::1

It's important to put DNS name in the SAN and not the CN, because both the IETF and the CA/Browser Forums specify the practice. They also specify that DNS names in the CN are deprecated (but not prohibited). If you put a DNS name in the CN, then it must be included in the SAN under the CA/B policies. So you can't avoid using the Subject Alternate Name.

If you don't do put DNS names in the SAN, then the certificate will fail to validate under a browser and other user agents which follow the CA/Browser Forum guidelines.

Related: browsers follow the CA/Browser Forum policies; and not the IETF policies. That's one of the reasons a certificate created with OpenSSL (which generally follows the IETF) sometimes does not validate under a browser (browsers follow the CA/B). They are different standards, they have different issuing policies and different validation requirements.

Create a self signed certificate (notice the addition of -x509 option):

openssl req -config example-com.conf -new -x509 -sha256 -newkey rsa:2048 -nodes \
    -keyout example-com.key.pem -days 365 -out example-com.cert.pem

Create a signing request (notice the lack of -x509 option):

openssl req -config example-com.conf -new -sha256 -newkey rsa:2048 -nodes \
    -keyout example-com.key.pem -days 365 -out example-com.req.pem

Print a self-signed certificate:

openssl x509 -in example-com.cert.pem -text -noout

Print a signing request:

openssl req -in example-com.req.pem -text -noout

Configuration file (passed via -config option)

[ req ]
default_bits        = 2048
default_keyfile     = server-key.pem
distinguished_name  = subject
req_extensions      = req_ext
x509_extensions     = x509_ext
string_mask         = utf8only

# The Subject DN can be formed using X501 or RFC 4514 (see RFC 4519 for a description).
#   Its sort of a mashup. For example, RFC 4514 does not provide emailAddress.
[ subject ]
countryName         = Country Name (2 letter code)
countryName_default     = US

stateOrProvinceName     = State or Province Name (full name)
stateOrProvinceName_default = NY

localityName            = Locality Name (eg, city)
localityName_default        = New York

organizationName         = Organization Name (eg, company)
organizationName_default    = Example, LLC

# Use a friendly name here because it's presented to the user. The server's DNS
#   names are placed in Subject Alternate Names. Plus, DNS names here is deprecated
#   by both IETF and CA/Browser Forums. If you place a DNS name here, then you
#   must include the DNS name in the SAN too (otherwise, Chrome and others that
#   strictly follow the CA/Browser Baseline Requirements will fail).
commonName          = Common Name (e.g. server FQDN or YOUR name)
commonName_default      = Example Company

emailAddress            = Email Address
emailAddress_default        = test@example.com

# Section x509_ext is used when generating a self-signed certificate. I.e., openssl req -x509 ...
[ x509_ext ]

subjectKeyIdentifier        = hash
authorityKeyIdentifier    = keyid,issuer

# You only need digitalSignature below. *If* you don't allow
#   RSA Key transport (i.e., you use ephemeral cipher suites), then
#   omit keyEncipherment because that's key transport.
basicConstraints        = CA:FALSE
keyUsage            = digitalSignature, keyEncipherment
subjectAltName          = @alternate_names
nsComment           = "OpenSSL Generated Certificate"

# RFC 5280, Section 4.2.1.12 makes EKU optional
#   CA/Browser Baseline Requirements, Appendix (B)(3)(G) makes me confused
#   In either case, you probably only need serverAuth.
# extendedKeyUsage    = serverAuth, clientAuth

# Section req_ext is used when generating a certificate signing request. I.e., openssl req ...
[ req_ext ]

subjectKeyIdentifier        = hash

basicConstraints        = CA:FALSE
keyUsage            = digitalSignature, keyEncipherment
subjectAltName          = @alternate_names
nsComment           = "OpenSSL Generated Certificate"

# RFC 5280, Section 4.2.1.12 makes EKU optional
#   CA/Browser Baseline Requirements, Appendix (B)(3)(G) makes me confused
#   In either case, you probably only need serverAuth.
# extendedKeyUsage    = serverAuth, clientAuth

[ alternate_names ]

DNS.1       = example.com
DNS.2       = www.example.com
DNS.3       = mail.example.com
DNS.4       = ftp.example.com

# Add these if you need them. But usually you don't want them or
#   need them in production. You may need them for development.
# DNS.5       = localhost
# DNS.6       = localhost.localdomain
# DNS.7       = 127.0.0.1

# IPv6 localhost
# DNS.8     = ::1

You may need to do the following for Chrome. Otherwise Chrome may complain a Common Name is invalid (ERR_CERT_COMMON_NAME_INVALID). I'm not sure what the relationship is between an IP address in the SAN and a CN in this instance.

# IPv4 localhost
# IP.1       = 127.0.0.1

# IPv6 localhost
# IP.2     = ::1

There are other rules concerning the handling of DNS names in X.509/PKIX certificates. Refer to these documents for the rules:

RFC 5280, Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile

RFC 6125, Representation and Verification of Domain-Based Application Service Identity within Internet Public Key Infrastructure Using X.509 (PKIX) Certificates in the Context of Transport Layer Security (TLS)

RFC 6797, Appendix A, HTTP Strict Transport Security (HSTS)

RFC 7469, Public Key Pinning Extension for HTTP

CA/Browser Forum Baseline Requirements

CA/Browser Forum Extended Validation Guidelines

RFC 6797 and RFC 7469 are listed, because they are more restrictive than the other RFCs and CA/B documents. RFCs 6797 and 7469 do not allow an IP address, either.


Is it possible to use wildcards in the alternate_names section? Particularly sub-sub domains. I have a question referencing this answer here: serverfault.com/questions/711596/…
I've just replied to his specific question. I think doesn't make sense to add this long security description when the answer was so simple
@diegows - your answer is not complete or correct. The reason it is not correct is discussed in the long post you don't want to read :)
Thanks! I found your post very helpful. FYI I was recently playing with vault and found it insisted on IP.x 127.0.0.1 rather than DNS.x 127... I didn't check if this is in the standard or not.
Thank you @jww. You said, "1. Create your own authority (i.e, become a CA)", then said, "5. Install the CA certificate on the client". If the root key became compromised, a malicious person could sign a cert for any domain with that key, and if they trick you into going to their website, they can now do a man-in-the-middle attack. Is there a way to create the root CA such that it can only sign intermediary CAs and not certificates? Then you can protect your intermediary CA with a name constraint.
m
miken32

As of 2022 with OpenSSL ≥ 1.1.1, the following command serves all your needs, including Subject Alternate Name (SAN):

openssl req -x509 -newkey rsa:4096 -sha256 -days 3650 -nodes \
  -keyout example.key -out example.crt -subj "/CN=example.com" \
  -addext "subjectAltName=DNS:example.com,DNS:www.example.net,IP:10.0.0.1"

On old systems with OpenSSL ≤ 1.1.0, such as Debian ≤ 9 or CentOS ≤ 7, a longer version of this command needs to be used:

openssl req -x509 -newkey rsa:4096 -sha256 -days 3650 -nodes \
  -keyout example.key -out example.crt -extensions san -config \
  <(echo "[req]"; 
    echo distinguished_name=req; 
    echo "[san]"; 
    echo subjectAltName=DNS:example.com,DNS:www.example.net,IP:10.0.0.1
    ) \
  -subj "/CN=example.com"

Either command creates a certificate that is

valid for the (sub)domains example.com and www.example.net (SAN),

also valid for the IP address 10.0.0.1 (SAN),

relatively strong (as of 2022) and

valid for 3650 days (~10 years).

The following files are generated:

Private key: example.key

Certificate: example.crt

All information is provided at the command line. There is no interactive input that annoys you. There are no config files you have to mess around with. All necessary steps are executed by a single OpenSSL invocation: from private key generation up to the self-signed certificate.

Remark #1: Crypto parameters

Since the certificate is self-signed and needs to be accepted by users manually, it doesn't make sense to use a short expiration or weak cryptography.

In the future, you might want to use more than 4096 bits for the RSA key and a hash algorithm stronger than sha256, but as of 2022 these are sane values. They are sufficiently strong while being supported by all modern browsers.

Remark #2: Parameter "-nodes"

Theoretically you could leave out the -nodes parameter (which means "no DES encryption"), in which case example.key would be encrypted with a password. However, this is almost never useful for a server installation, because you would either have to store the password on the server as well, or you'd have to enter it manually on each reboot.

Remark #3: See also

Provide subjectAltName to openssl directly on command line

How to add multiple email addresses to an SSL certificate via the command line?

More information about MSYS_NO_PATHCONV


I tried to use the oneliner #2 (modern) on windows in mingw64, and I faced a bug with -subj parameter. ` $ openssl req -x509 -newkey rsa:4096 -sha256 -days 3650 -nodes -keyout localhost.key -out localhost.crt -subj '/CN=localhost' -addext subjectAltName=DNS:localhost,IP:127.0.0.1 Generating a RSA private key [...] writing new private key to 'localhost.key' ----- name is expected to be in the format /type0=value0/type1=value1/type2=... where characters may be escaped by \. This name is not in that format: 'C:/Program Files/Git/CN=localhost' problems making Certificate Request `
I couldn't figure out what exactly was to blame in the arg /CN=localhost expanding to C:/Program Files/Git/CN=localhost , so I just ran the whole command in plain cmd.exe and it worked just fine. Just in case someone is struggling with this one.
@FranklinYu Are you sure that rsa:2048 will be enough in 10 years from now? Because that's the validity period. As explained, it doesn't make sense to use short expiration or weak crypto. Most 2048-bit RSA keys have a validity period of 1-3 years at most. Regarding OpenSSL 1.1.1, I'm still leaving sha256 in there, so it's more explicit and obvious to change if you want a stronger hash.
If you're using git bash on windows, like @YuriyPozniak, you will get the error he listed where /CN=localhost is being expanded to C:/Progra Files/Git/CN=localhost. If you add an extra /, then the expansion won't occur. //CN=localhost
1000 +1s for creating a "one-liner" that uses the new required SAN without having to create a long-winded config file with a lot of boilerplate. Well done!
P
Peter Mortensen

Here are the options described in @diegows's answer, described in more detail, from the documentation:

openssl req -x509 -newkey rsa:2048 -keyout key.pem -out cert.pem -days XXX

req PKCS#10 certificate request and certificate generating utility. -x509 this option outputs a self signed certificate instead of a certificate request. This is typically used to generate a test certificate or a self signed root CA. -newkey arg this option creates a new certificate request and a new private key. The argument takes one of several forms. rsa:nbits, where nbits is the number of bits, generates an RSA key nbits in size. -keyout filename this gives the filename to write the newly created private key to. -out filename This specifies the output filename to write to or standard output by default. -days n when the -x509 option is being used this specifies the number of days to certify the certificate for. The default is 30 days. -nodes if this option is specified then if a private key is created it will not be encrypted.

The documentation is actually more detailed than the above; I just summarized it here.


The XXX in the original command should be replaced with the 'number of days to certify the certificate for'. The default is 30 days. For example, -days XXX becomes -days 365 if you want your cert to be valid for 365 days. See the docs for more.
Thanks for adding the documentation. This IBM link on creating a self-signed certificate using command which seems identical to this answer
P
Peter Mortensen

I can't comment, so I will put this as a separate answer. I found a few issues with the accepted one-liner answer:

The one-liner includes a passphrase in the key.

The one-liner uses SHA-1 which in many browsers throws warnings in console.

Here is a simplified version that removes the passphrase, ups the security to suppress warnings and includes a suggestion in comments to pass in -subj to remove the full question list:

openssl genrsa -out server.key 2048
openssl rsa -in server.key -out server.key
openssl req -sha256 -new -key server.key -out server.csr -subj '/CN=localhost'
openssl x509 -req -sha256 -days 365 -in server.csr -signkey server.key -out server.crt

Replace 'localhost' with whatever domain you require. You will need to run the first two commands one by one as OpenSSL will prompt for a passphrase.

To combine the two into a .pem file:

cat server.crt server.key > cert.pem

I needed a dev certificate for github.com/molnarg/node-http2 and this answer is just the best.
To combine the certificate and the key in a single file: cat server.crt server.key >foo-cert.pem. Works with the example in openssl-1.0.2d/demos/ssl/
The cert I generated this way is still using SHA1.
Tks, works great to create a self signed certificate on FreeBSD 10 OpenLDAP 2.4 with TLS
What about the key.pem file?
v
vcsjones

Modern browsers now throw a security error for otherwise well-formed self-signed certificates if they are missing a SAN (Subject Alternate Name). OpenSSL does not provide a command-line way to specify this, so many developers' tutorials and bookmarks are suddenly outdated.

The quickest way to get running again is a short, stand-alone conf file:

Create an OpenSSL config file (example: req.cnf) [req] distinguished_name = req_distinguished_name x509_extensions = v3_req prompt = no [req_distinguished_name] C = US ST = VA L = SomeCity O = MyCompany OU = MyDivision CN = www.company.com [v3_req] keyUsage = critical, digitalSignature, keyAgreement extendedKeyUsage = serverAuth subjectAltName = @alt_names [alt_names] DNS.1 = www.company.com DNS.2 = company.com DNS.3 = company.net Create the certificate referencing this config file openssl req -x509 -nodes -days 730 -newkey rsa:2048 \ -keyout cert.key -out cert.pem -config req.cnf -sha256

Example config from https://support.citrix.com/article/CTX135602


It worked for me after removing the last parameter -extensions 'v3_req' which was causing an error. Using OpenSSL for windows. Finally, I manage to fix this issue! Thanks.
@Kyopaxa you're right - that parameter is redundant with line 3 of the cnf file; updated.
Solid way. Thanks. I'd suggest adding -sha256.
You can now specify the SAN on the command line with -extension 'subjectAltName = DNS:dom.ain, DNS:oth.er' see github.com/openssl/openssl/pull/4986
Looks like this option is called -addext now.
P
Peter Mortensen

I would recommend to add the -sha256 parameter, to use the SHA-2 hash algorithm, because major browsers are considering to show "SHA-1 certificates" as not secure.

The same command line from the accepted answer - @diegows with added -sha256

openssl req -x509 -sha256 -newkey rsa:2048 -keyout key.pem -out cert.pem -days XXX

More information in Google Security blog.

Update May 2018. As many noted in the comments that using SHA-2 does not add any security to a self-signed certificate. But I still recommend using it as a good habit of not using outdated / insecure cryptographic hash functions. Full explanation is available in Why is it fine for certificates above the end-entity certificate to be SHA-1 based?.


If it's a self signed key, it's going to generate browser errors anyway, so this doesn't really matter
@Mark, it matters, because SHA-2 is more secure
Opening the certificate in windows after renaming the cert.pem to cert.cer says the fingerprint algorithm still is Sha1, but the signature hash algorithm is sha256.
"World-class encryption * zero authentication = zero security" gerv.net/security/self-signed-certs
Note that the signature algorithm used on a self-signed certificate is irrelevant in deciding whether it's trustworthy or not. Root CA certs are self-signed. and as of May 2018, there are still many active root CA certificates that are SHA-1 signed. Because it doesn't matter if a certificate trusts itself, nor how that certificate verifies that trust. You either trust the root/self-signed cert for who it says it is, or you don't. See security.stackexchange.com/questions/91913/…
D
Doug

I can`t comment so I add a separate answer. I tried to create a self-signed certificate for NGINX and it was easy, but when I wanted to add it to Chrome white list I had a problem. And my solution was to create a Root certificate and signed a child certificate by it.

So step by step. Create file config_ssl_ca.cnf Notice, config file has an option basicConstraints=CA:true which means that this certificate is supposed to be root.

This is a good practice, because you create it once and can reuse.

[ req ]
default_bits = 2048

prompt = no
distinguished_name=req_distinguished_name
req_extensions = v3_req

[ req_distinguished_name ]
countryName=UA
stateOrProvinceName=root region
localityName=root city
organizationName=Market(localhost)
organizationalUnitName=roote department
commonName=market.localhost
emailAddress=root_email@root.localhost

[ alternate_names ]
DNS.1        = market.localhost
DNS.2        = www.market.localhost
DNS.3        = mail.market.localhost
DNS.4        = ftp.market.localhost
DNS.5        = *.market.localhost

[ v3_req ]
keyUsage=digitalSignature
basicConstraints=CA:true
subjectKeyIdentifier = hash
subjectAltName = @alternate_names

Next config file for your child certificate will be call config_ssl.cnf.

[ req ]
default_bits = 2048

prompt = no
distinguished_name=req_distinguished_name
req_extensions = v3_req

[ req_distinguished_name ]
countryName=UA
stateOrProvinceName=Kyiv region
localityName=Kyiv
organizationName=market place
organizationalUnitName=market place department
commonName=market.localhost
emailAddress=email@market.localhost

[ alternate_names ]
DNS.1        = market.localhost
DNS.2        = www.market.localhost
DNS.3        = mail.market.localhost
DNS.4        = ftp.market.localhost
DNS.5        = *.market.localhost

[ v3_req ]
keyUsage=digitalSignature
basicConstraints=CA:false
subjectAltName = @alternate_names
subjectKeyIdentifier = hash

The first step - create Root key and certificate

openssl genrsa -out ca.key 2048
openssl req -new -x509 -key ca.key -out ca.crt -days 365 -config config_ssl_ca.cnf

The second step creates child key and file CSR - Certificate Signing Request. Because the idea is to sign the child certificate by root and get a correct certificate

openssl genrsa -out market.key 2048
openssl req -new -sha256 -key market.key -config config_ssl.cnf -out market.csr

Open Linux terminal and do this command

echo 00 > ca.srl
touch index.txt

The ca.srl text file containing the next serial number to use in hex. Mandatory. This file must be present and contain a valid serial number.

Last Step, create one more config file and call it config_ca.cnf

# we use 'ca' as the default section because we're usign the ca command
[ ca ]
default_ca = my_ca

[ my_ca ]
#  a text file containing the next serial number to use in hex. Mandatory.
#  This file must be present and contain a valid serial number.
serial = ./ca.srl

# the text database file to use. Mandatory. This file must be present though
# initially it will be empty.
database = ./index.txt

# specifies the directory where new certificates will be placed. Mandatory.
new_certs_dir = ./

# the file containing the CA certificate. Mandatory
certificate = ./ca.crt

# the file contaning the CA private key. Mandatory
private_key = ./ca.key

# the message digest algorithm. Remember to not use MD5
default_md = sha256

# for how many days will the signed certificate be valid
default_days = 365

# a section with a set of variables corresponding to DN fields
policy = my_policy

# MOST IMPORTANT PART OF THIS CONFIG
copy_extensions = copy

[ my_policy ]
# if the value is "match" then the field value must match the same field in the
# CA certificate. If the value is "supplied" then it must be present.
# Optional means it may be present. Any fields not mentioned are silently
# deleted.
countryName = match
stateOrProvinceName = supplied
organizationName = supplied
commonName = market.localhost
organizationalUnitName = optional
commonName = supplied

You may ask, why so difficult, why we must create one more config to sign child certificate by root. The answer is simple because child certificate must have a SAN block - Subject Alternative Names. If we sign the child certificate by "openssl x509" utils, the Root certificate will delete the SAN field in child certificate. So we use "openssl ca" instead of "openssl x509" to avoid the deleting of the SAN field. We create a new config file and tell it to copy all extended fields copy_extensions = copy.

openssl ca -config config_ca.cnf -out market.crt -in market.csr

The program asks you 2 questions:

Sign the certificate? Say "Y" 1 out of 1 certificate requests certified, commit? Say "Y"

In terminal you can see a sentence with the word "Database", it means file index.txt which you create by the command "touch". It will contain all information by all certificates you create by "openssl ca" util. To check the certificate valid use:

openssl rsa -in market.key -check

If you want to see what inside in CRT:

openssl x509 -in market.crt -text -noout

If you want to see what inside in CSR:

openssl req -in market.csr -noout -text 

Although, this process looks complicated, this is exactly what we need for .dev domain, as this domain does not support self-signed certificates and Chrome and Firefox are forcing HSTS. What I did is followed this steps, which is creating CA, creating a certificate and signing it with my CA and at the end trusting my CA in the browser. Thanks.
Your common name is wrong. Not firstname/lastname. its your domain cn i.e. www.yoursite.com . see ssl.com/faqs/common-name
no problem. there are some documents which also say name (yourname) which is a bit misleading. but common name should be the actual domain. in this sense it would be (your"domain"name) they are trying to say. when running thru with interactive method of creating the certs, it does say cn=domain example. so commonname should be domain
P
Peter Mortensen

This is the script I use on local boxes to set the SAN (subjectAltName) in self-signed certificates.

This script takes the domain name (example.com) and generates the SAN for *.example.com and example.com in the same certificate. The sections below are commented. Name the script (e.g. generate-ssl.sh) and give it executable permissions. The files will be written to the same directory as the script.

Chrome 58 an onward requires SAN to be set in self-signed certificates.

#!/usr/bin/env bash

# Set the TLD domain we want to use
BASE_DOMAIN="example.com"

# Days for the cert to live
DAYS=1095

# A blank passphrase
PASSPHRASE=""

# Generated configuration file
CONFIG_FILE="config.txt"

cat > $CONFIG_FILE <<-EOF
[req]
default_bits = 2048
prompt = no
default_md = sha256
x509_extensions = v3_req
distinguished_name = dn

[dn]
C = CA
ST = BC
L = Vancouver
O = Example Corp
OU = Testing Domain
emailAddress = webmaster@$BASE_DOMAIN
CN = $BASE_DOMAIN

[v3_req]
subjectAltName = @alt_names

[alt_names]
DNS.1 = *.$BASE_DOMAIN
DNS.2 = $BASE_DOMAIN
EOF

# The file name can be anything
FILE_NAME="$BASE_DOMAIN"

# Remove previous keys
echo "Removing existing certs like $FILE_NAME.*"
chmod 770 $FILE_NAME.*
rm $FILE_NAME.*

echo "Generating certs for $BASE_DOMAIN"

# Generate our Private Key, CSR and Certificate
# Use SHA-2 as SHA-1 is unsupported from Jan 1, 2017

openssl req -new -x509 -newkey rsa:2048 -sha256 -nodes -keyout "$FILE_NAME.key" -days $DAYS -out "$FILE_NAME.crt" -passin pass:$PASSPHRASE -config "$CONFIG_FILE"

# OPTIONAL - write an info to see the details of the generated crt
openssl x509 -noout -fingerprint -text < "$FILE_NAME.crt" > "$FILE_NAME.info"

# Protect the key
chmod 400 "$FILE_NAME.key"

This script also writes an information file, so you can inspect the new certificate and verify the SAN is set properly.

                ...
                28:dd:b8:1e:34:b5:b1:44:1a:60:6d:e3:3c:5a:c4:
                da:3d
            Exponent: 65537 (0x10001)
    X509v3 extensions:
        X509v3 Subject Alternative Name: 
            DNS:*.example.com, DNS:example.com
Signature Algorithm: sha256WithRSAEncryption
     3b:35:5a:d6:9e:92:4f:fc:f4:f4:87:78:cd:c7:8d:cd:8c:cc:
     ...

If you are using Apache, then you can reference the above certificate in your configuration file like so:

<VirtualHost _default_:443>
    ServerName example.com
    ServerAlias www.example.com
    DocumentRoot /var/www/htdocs

    SSLEngine on
    SSLCertificateFile path/to/your/example.com.crt
    SSLCertificateKeyFile path/to/your/example.com.key
</VirtualHost>

Remember to restart your Apache (or Nginx, or IIS) server for the new certificate to take effect.


Works on macOS High Siera and Chrome 58
I'm still not sure how the CN affects the overall setup? I'm attempting to run this as localhost or 127.0.0.1:port# what would be the corresponding CN for something like this.
@DJ2 I would set BASE_DOMAIN=“localhost”
P
Peter Mortensen

2017 one-liner:

openssl req \
-newkey rsa:2048 \
-x509 \
-nodes \
-keyout server.pem \
-new \
-out server.pem \
-subj /CN=localhost \
-reqexts SAN \
-extensions SAN \
-config <(cat /System/Library/OpenSSL/openssl.cnf \
    <(printf '[SAN]\nsubjectAltName=DNS:localhost')) \
-sha256 \
-days 3650

This also works in Chrome 57, as it provides the SAN, without having another configuration file. It was taken from an answer here.

This creates a single .pem file that contains both the private key and cert. You can move them to separate .pem files if needed.


For Linux users you'll need to change that path for the config. e.g. on current Ubuntu /etc/ssl/openssl.conf works
For a one-liner that doesn't require you to specify the openssl.cnf location, see: stackoverflow.com/a/41366949/19163
C
Community

One-liner version 2017:

CentOS:

openssl req -x509 -nodes -sha256 -newkey rsa:2048 \
-keyout localhost.key -out localhost.crt \
-days 3650 \
-subj "CN=localhost" \
-reqexts SAN -extensions SAN \
-config <(cat /etc/pki/tls/openssl.cnf <(printf "\n[SAN]\nsubjectAltName=IP:127.0.0.1,DNS:localhost"))

Ubuntu:

openssl req -x509 -nodes -sha256 -newkey rsa:2048 \
-keyout localhost.key -out localhost.crt \
-days 3650 \
-subj "/CN=localhost" \
-reqexts SAN -extensions SAN \
-config <(cat /etc/ssl/openssl.cnf <(printf "\n[SAN]\nsubjectAltName=IP:127.0.0.1,DNS:localhost"))

Edit: added prepending Slash to 'subj' option for Ubuntu.


P
Peter Mortensen

One liner FTW. I like to keep it simple. Why not use one command that contains ALL the arguments needed? This is how I like it - this creates an x509 certificate and its PEM key:

openssl req -x509 \
 -nodes -days 365 -newkey rsa:4096 \
 -keyout self.key.pem \
 -out self-x509.crt \
 -subj "/C=US/ST=WA/L=Seattle/CN=example.com/emailAddress=someEmail@gmail.com"

That single command contains all the answers you would normally provide for the certificate details. This way you can set the parameters and run the command, get your output - then go for coffee.

>> More here <<


All the arguments except for SANs... @vog's answer covers that as well (and predate this) (This has a more complete "Subject" field filled in though...) (Not a big fan of the one year expiry either)
vog's answer. Linked, because usernames are neither unique nor immutable. "vog" could change to "scoogie" at any point in time.
g
gavenkoa

openssl allows to generate self-signed certificate by a single command (-newkey instructs to generate a private key and -x509 instructs to issue a self-signed certificate instead of a signing request)::

openssl req -x509 -newkey rsa:4096 \
-keyout my.key -passout pass:123456 -out my.crt \
-days 365 \
-subj /CN=localhost/O=home/C=US/emailAddress=me@mail.internal \
-addext "subjectAltName = DNS:localhost,DNS:web.internal,email:me@mail.internal" \
-addext keyUsage=digitalSignature -addext extendedKeyUsage=serverAuth

You can generate a private key and construct a self-signing certificate in separate steps::

openssl genrsa -out my.key -passout pass:123456 2048

openssl req -x509 \
-key my.key -passin pass:123456 -out my.csr \
-days 3650 \
-subj /CN=localhost/O=home/C=US/emailAddress=me@mail.internal \
-addext "subjectAltName = DNS:localhost,DNS:web.internal,email:me@mail.internal" \
-addext keyUsage=digitalSignature -addext extendedKeyUsage=serverAuth

Review the resulting certificate::

openssl x509 -text -noout -in my.crt

Java keytool creates PKCS#12 store::

keytool -genkeypair -keystore my.p12 -alias master \
-storetype pkcs12 -keyalg RSA -keysize 2048 -validity 3650 \
-storepass 123456 \
-dname "CN=localhost,O=home,C=US" \
-ext 'san=dns:localhost,dns:web.internal,email:me@mail.internal'

To export the self-signed certificate::

keytool -exportcert -keystore my.p12 -file my.crt \
-alias master -rfc -storepass 123456

Review the resulting certificate::

keytool -printcert -file my.crt

certtool from GnuTLS doesn't allow passing different attributes from CLI. I don't like to mess with config files ((


I cannot stress that enough!!!!!!! extendedKeyUsage = serverAuth, clientAuth is what got me the button "Proceed to localhost (unsafe)"
P
Peter Mortensen

You have the general procedure correct. The syntax for the command is below.

openssl req -new -key {private key file} -out {output file}

However, the warnings are displayed, because the browser was not able to verify the identify by validating the certificate with a known Certificate Authority (CA).

As this is a self-signed certificate there is no CA and you can safely ignore the warning and proceed. Should you want to get a real certificate that will be recognizable by anyone on the public Internet then the procedure is below.

Generate a private key Use that private key to create a CSR file Submit CSR to CA (Verisign or others, etc.) Install received cert from CA on web server Add other certs to authentication chain depending on the type cert

I have more details about this in a post at Securing the Connection: Creating a Security Certificate with OpenSSL


3
3 revs, 3 users 80%

Generate keys I am using /etc/mysql for cert storage because /etc/apparmor.d/usr.sbin.mysqld contains /etc/mysql/*.pem r. sudo su - cd /etc/mysql openssl genrsa -out ca-key.pem 2048; openssl req -new -x509 -nodes -days 1000 -key ca-key.pem -out ca-cert.pem; openssl req -newkey rsa:2048 -days 1000 -nodes -keyout server-key.pem -out server-req.pem; openssl x509 -req -in server-req.pem -days 1000 -CA ca-cert.pem -CAkey ca-key.pem -set_serial 01 -out server-cert.pem; openssl req -newkey rsa:2048 -days 1000 -nodes -keyout client-key.pem -out client-req.pem; openssl x509 -req -in client-req.pem -days 1000 -CA ca-cert.pem -CAkey ca-key.pem -set_serial 01 -out client-cert.pem; Add configuration /etc/mysql/my.cnf [client] ssl-ca=/etc/mysql/ca-cert.pem ssl-cert=/etc/mysql/client-cert.pem ssl-key=/etc/mysql/client-key.pem [mysqld] ssl-ca=/etc/mysql/ca-cert.pem ssl-cert=/etc/mysql/server-cert.pem ssl-key=/etc/mysql/server-key.pem

On my setup, Ubuntu server logged to: /var/log/mysql/error.log

Follow up notes:

SSL error: Unable to get certificate from '...' MySQL might be denied read access to your certificate file if it is not in apparmors configuration. As mentioned in the previous steps^, save all our certificates as .pem files in the /etc/mysql/ directory which is approved by default by apparmor (or modify your apparmor/SELinux to allow access to wherever you stored them.)

SSL error: Unable to get private key Your MySQL server version may not support the default rsa:2048 format Convert generated rsa:2048 to plain rsa with: openssl rsa -in server-key.pem -out server-key.pem openssl rsa -in client-key.pem -out client-key.pem

Check if local server supports SSL: mysql -u root -p mysql> show variables like "%ssl%"; +---------------+----------------------------+ | Variable_name | Value | +---------------+----------------------------+ | have_openssl | YES | | have_ssl | YES | | ssl_ca | /etc/mysql/ca-cert.pem | | ssl_capath | | | ssl_cert | /etc/mysql/server-cert.pem | | ssl_cipher | | | ssl_key | /etc/mysql/server-key.pem | +---------------+----------------------------+

Verifying a connection to the database is SSL encrypted: Verifying connection When logged in to the MySQL instance, you can issue the query: show status like 'Ssl_cipher'; If your connection is not encrypted, the result will be blank: mysql> show status like 'Ssl_cipher'; +---------------+-------+ | Variable_name | Value | +---------------+-------+ | Ssl_cipher | | +---------------+-------+ 1 row in set (0.00 sec) Otherwise, it would show a non-zero length string for the cypher in use: mysql> show status like 'Ssl_cipher'; +---------------+--------------------+ | Variable_name | Value | +---------------+--------------------+ | Ssl_cipher | DHE-RSA-AES256-SHA | +---------------+--------------------+ 1 row in set (0.00 sec)

Require ssl for specific user's connection ('require ssl'): SSL Tells the server to permit only SSL-encrypted connections for the account. GRANT ALL PRIVILEGES ON test.* TO 'root'@'localhost' REQUIRE SSL; To connect, the client must specify the --ssl-ca option to authenticate the server certificate, and may additionally specify the --ssl-key and --ssl-cert options. If neither --ssl-ca option nor --ssl-capath option is specified, the client does not authenticate the server certificate.

SSL

Alternate link: Lengthy tutorial in Secure PHP Connections to MySQL with SSL.


-1; this is largely tangential to the question asked, and also does a bad job of making clear where its quotes are from.
This shows provisioning CA, Server/Client certs signed by the CA, configure them for reading by mysqld on a host with apparmor. It exemplifies a rather useless case of hosting the ca, server, and client on the same machine, and dangerously exposing that ca's authority to the mysqld process. This setup doesn't really make sense other than to test ssl configuration in a test environment. For operating an internal CA, I would recommend the gnuttls toolchain over openssl help.ubuntu.com/community/GnuTLS and having a good understanding of tls before working around the mysqld+apparmor case
P
Peter Jirak Eldritch

As has been discussed in detail, self-signed certificates are not trusted for the Internet. You can add your self-signed certificate to many but not all browsers. Alternatively you can become your own certificate authority.

The primary reason one does not want to get a signed certificate from a certificate authority is cost -- Symantec charges between $995 - $1,999 per year for certificates -- just for a certificate intended for internal network, Symantec charges $399 per year. That cost is easy to justify if you are processing credit card payments or work for the profit center of a highly profitable company. It is more than many can afford for a personal project one is creating on the internet, or for a non-profit running on a minimal budget, or if one works in a cost center of an organization -- cost centers always try to do more with less.

An alternative is to use certbot (see about certbot). Certbot is an easy-to-use automatic client that fetches and deploys SSL/TLS certificates for your web server.

If you setup certbot, you can enable it to create and maintain a certificate for you issued by the Let’s Encrypt certificate authority.

I did this over the weekend for my organization. I installed the required packages for certbot on my server (Ubuntu 16.04) and then ran the command necessary to setup and enable certbot. One likely needs a DNS plugin for certbot - we are presently using DigitalOcean though may be migrating to another service soon.

Note that some of the instructions were not quite right and took a little poking and time with Google to figure out. This took a fair amount of my time the first time but now I think I could do it in minutes.

For DigitalOcean, one area I struggled was when I was prompted to input the path to your DigitalOcean credentials INI file. What the script is referring to is the Applications & API page and the Tokens/Key tab on that page. You need to have or generate a personal access token (read and write) for DigitalOcean's API -- this is a 65 character hexadecimal string. This string then needs to be put into a file on the webserver from which you are running certbot. That file can have a comment as its first line (comments start with #). The seccond line is:

dns_digitalocean_token = 0000111122223333444455556666777788889999aaaabbbbccccddddeeeeffff

Once I figured out how to set up a read+write token for DigitalOcean's API, it was pretty easy to use certbot to setup a wildcard certificate. Note that one does not have to setup a wildcard certificate, one may instead specify each domain and sub-domain that one wants the certificate to appply to. It was the wildcard certificate that required the credentials INI file that contained the personal access token from DigitalOcean.

Note that public key certificates (also known as identity certificates or SSL certificates) expire and require renewal. Thus you will need to renew your certificate on a periodic (reoccurring) basis. The certbot documentation covers renewing certificates.

My plan is to write a script to use the openssl command to get my certificate's expiration date and to trigger renewal when it is 30 days or less until it expires. I will then add this script to cron and run it once per day.

Here is the command to read your certificate's expiration date:

root@prod-host:~# /usr/bin/openssl x509 -enddate -noout -in path-to-certificate-pem-file
notAfter=May 25 19:24:12 2019 GMT

L
Leonardo Pineda

this worked for me

openssl req -x509 -nodes -subj '/CN=localhost'  -newkey rsa:4096 -keyout ./sslcert/key.pem -out ./sslcert/cert.pem -days 365

server.js

var fs = require('fs');
var path = require('path');
var http = require('http');
var https = require('https');
var compression = require('compression');
var express = require('express');
var app = express();

app.use(compression());
app.use(express.static(__dirname + '/www'));    

app.get('/*', function(req,res) {
  res.sendFile(path.join(__dirname+'/www/index.html'));
});

// your express configuration here

var httpServer = http.createServer(app);
var credentials = {
    key: fs.readFileSync('./sslcert/key.pem', 'utf8'),
    cert: fs.readFileSync('./sslcert/cert.pem', 'utf8')
};
var httpsServer = https.createServer(credentials, app);

httpServer.listen(8080);
httpsServer.listen(8443);

console.log(`RUNNING ON  http://127.0.0.1:8080`);
console.log(`RUNNING ON  http://127.0.0.1:8443`);

J
JohnnyJS

After much of going around, playing with various solutions, still I faced the problem that issuing a self-signed certificate for localhost, gave me error

ERR_CERT_INVALID

When expanding the details, chrome said:

You cannot visit localhost right now because the website sent scrambled credentials...

And the only ugly way to get through is to type (directly in this screen, without seeing any cursor for the text) :

(type in the keyboard) thisisunsafe

Which let me proceed.

Until I found extendedKeyUsage = serverAuth, clientAuth

TL;DR

openssl genrsa -out localhost.key 2048 openssl req -key localhost.key -new -out localhost.csr (click enter on everything and just fill in the common name (CN) with localhost or your other FQDN. put the following in a file named v3.ext (edit whatever you need):

subjectKeyIdentifier   = hash
authorityKeyIdentifier = keyid:always,issuer:always
basicConstraints       = CA:TRUE
keyUsage               = digitalSignature, nonRepudiation, keyEncipherment, dataEncipherment, keyAgreement, keyCertSign
extendedKeyUsage       = serverAuth, clientAuth
subjectAltName         = DNS:localhost, DNS:localhost.localdomain
issuerAltName          = issuer:copy

openssl x509 -req -in localhost.csr -signkey localhost.key -out localhost.pem -days 3650 -sha256 -extfile v3.ext

And voilà! You can visit the website, expand "Advanced" and click "Proceed to localhost (unsafe)".


Maybe some smart fellow would be able to make all of this a nice one-liner...
what is the v3.ext file in your last command?
Edited the answer. look at point 4.
M
Maoz Zadok

Generate a key without password and certificate for 10 years, the short way:

openssl req  -x509 -nodes -new  -keyout server.key -out server.crt -days 3650 -subj "/C=/ST=/L=/O=/OU=web/CN=www.server.com"

for the flag -subj | -subject empty values are permitted -subj "/C=/ST=/L=/O=/OU=web/CN=www.server.com", but you can sets more details as you like:

C - Country Name (2 letter code)

ST - State

L - Locality Name (eg, city)

O - Organization Name

OU - Organizational Unit Name

CN - Common Name - required!


A
Anonymous

This very simple Python app that creates a self-signed certificate. Code:

from OpenSSL import crypto, SSL
from secrets import randbelow
print("Please know, if you make a mistake, you must restart the program.")
def cert_gen(
    emailAddress=input("Enter Email Address: "),
    commonName=input("Enter Common Name: "),
    countryName=input("Enter Country Name (2 characters): "),
    localityName=input("Enter Locality Name: "),
    stateOrProvinceName=input("Enter State of Province Name: "),
    organizationName=input("Enter Organization Name: "),
    organizationUnitName=input("Enter Organization Unit Name: "),
    serialNumber=randbelow(1000000),
    validityStartInSeconds=0,
    validityEndInSeconds=10*365*24*60*60,
    KEY_FILE = "private.key",
    CERT_FILE="selfsigned.crt"):
    #can look at generated file using openssl:
    #openssl x509 -inform pem -in selfsigned.crt -noout -text
    # create a key pair
    k = crypto.PKey()
    k.generate_key(crypto.TYPE_RSA, 4096)
    # create a self-signed cert
    cert = crypto.X509()
    cert.get_subject().C = countryName
    cert.get_subject().ST = stateOrProvinceName
    cert.get_subject().L = localityName
    cert.get_subject().O = organizationName
    cert.get_subject().OU = organizationUnitName
    cert.get_subject().CN = commonName
    cert.get_subject().emailAddress = emailAddress
    cert.set_serial_number(serialNumber)
    cert.gmtime_adj_notBefore(0)
    cert.gmtime_adj_notAfter(validityEndInSeconds)
    cert.set_issuer(cert.get_subject())
    cert.set_pubkey(k)
    cert.sign(k, 'sha512')
    with open(CERT_FILE, "wt") as f:
        f.write(crypto.dump_certificate(crypto.FILETYPE_PEM, cert).decode("utf-8"))
    with open(KEY_FILE, "wt") as f:
        f.write(crypto.dump_privatekey(crypto.FILETYPE_PEM, k).decode("utf-8"))
    print("GENERATED")
    input("Press enter to close program.")
cert_gen()

However, you still get the "certificate is not trusted" error. This is because of a few reasons:

It is self-signed/not verified (a verified certificate would need a CA (Certificate Authority), like Let's Encrypt to be trusted on all devices). It is not trusted on your machine. (this answer shows how you can make Windows trust your certificate).