This is a text-only version of the following page on https://raymii.org:
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Title       : 	OpenSSL get entire certificate chain from a domain or loop over entire chain in file
Author      : 	Remy van Elst
Date        : 	16-07-2024 18:30
URL         : 	https://raymii.org/s/snippets/OpenSSL_get_entire_certificate_chain_from_a_domain_or_use_all_certs_in_a_file.html
Format      : 	Markdown/HTML
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The `openssl x509` command can be used to get information from a certificate. If you supply a filename, the command will only use the topmost certificate in the file, not all certificates in the file, like in the case of a certificate chain. The `openssl s_client -connect` command can connect to a server and show all certificates served by that server. The command I'm providing in this snippet splits up all certificates found in a file or as the result of `openssl s_client` and allows `openssl x509` to loop over each one individually. 

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The command I use to print the entire certificate chain from a domain is the
following:


	OLDIFS=$IFS; IFS=':' certificates=$(openssl s_client -connect raymii.org:443 -showcerts -tlsextdebug 2>&1 </dev/null | sed -n '/-----BEGIN/,/-----END/{/-----BEGIN/ s/^/:/; p}'); for certificate in ${certificates#:}; do echo $certificate | openssl x509 -noout -subject -issuer  -ext subjectAltName; echo; done; IFS=$OLDIFS

Output:

	subject=CN = raymii.org
	issuer=C = GB, ST = Greater Manchester, L = Salford, O = Sectigo Limited, CN = Sectigo RSA Domain Validation Secure Server CA
	X509v3 Subject Alternative Name:
	    DNS:raymii.org, DNS:www.raymii.org

	subject=C = GB, ST = Greater Manchester, L = Salford, O = Sectigo Limited, CN = Sectigo RSA Domain Validation Secure Server CA
	issuer=C = US, ST = New Jersey, L = Jersey City, O = The USERTRUST Network, CN = USERTrust RSA Certification Authority
	No extensions in certificate

	subject=C = US, ST = New Jersey, L = Jersey City, O = The USERTRUST Network, CN = USERTrust RSA Certification Authority
	issuer=C = US, ST = New Jersey, L = Jersey City, O = The USERTRUST Network, CN = USERTrust RSA Certification Authority
	No extensions in certificate
	

If you have the certificates in a local file, for this example `chain.pem`, this is the command:

    OLDIFS=$IFS; IFS=':' certificates=$(sed -n '/-----BEGIN/,/-----END/{/-----BEGIN/ s/^/:/; p}' chain.pem); for certificate in ${certificates#:}; do echo $certificate | openssl x509 -noout -subject; echo; done; IFS=$OLDIFS

Output:

    subject=CN = raymii.org

    subject=C = GB, ST = Greater Manchester, L = Salford, O = Sectigo Limited, CN = Sectigo RSA Domain Validation Secure Server CA

    subject=C = US, ST = New Jersey, L = Jersey City, O = The USERTRUST Network, CN = USERTrust RSA Certification Authority


You can replace the `openssl x509 -noout -subject -issuer -ext subjectAltName`
by any option supported by `openssl x509`. For this example I choose to echo
the `subject`, `issuer` and `subjectAlternativeNames` but you get the gist. 


Here's a breakdown of what the script does:

- `OLDIFS=$IFS; IFS=':'` - This changes the Internal Field Separator (IFS) to
  `:`. The IFS is a special shell variable used for word splitting after
  expansion and to split lines into words with the read built-in command. The
  original `IFS` is saved in `OLDIFS` to restore it later.

- `certificates=$(openssl s_client [...] |
  sed -n '/-----BEG[...] s/^/:/; p}')` - This uses the
  `openssl` command to connect to `google.nl` on port 443 and extract the SSL
  certificates. The `sed` command is used to format the output so that each
  certificate starts with a `:`.

- `for certificate in ${certificates#:}; do echo [...]` - This loops over each
  certificate (split by `:` due to the `IFS`) and uses `openssl` to extract the
  subject alternative name, subject, and issuer of each certificate.

- `IFS=$OLDIFS` - This restores the original `IFS`.


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