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Extract Certificate Information with OpenSSL

Fetch the X.509 Public Key Certificate File

openssl s_client -connect google.com:443 -showcerts </dev/null | openssl x509 -outform pem > googlecert.pem

Decode the Entire Certificate

openssl x509 -in googlecert.pem -noout -text

Extract Specific Information from the Certificate

Extract the Subject

openssl x509 -in googlecert.pem -noout -subject subject=CN = *.google.com

Extract the Issuer

$ openssl x509 -in googlecert.pem -noout -issuer issuer=C = US, O = Google Trust Services LLC, CN = GTS CA 1C3

Extracting the Extension Fields

$ openssl x509 -in googlecert.pem -noout -ext subjectAltName X509v3 Subject Alternative Name: DNS:*.google.com, DNS:*.appengine.google.com, DNS:*.bdn.dev, DNS:*.cloud.google.com, DNS:*.crowdsource.google.com, DNS:*.datacompute.google.com, ...(truncated)

 

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