How to extract the RSA public key from a .cer and store it in a .pem using OpenSSL?

encryption openssl rsa pem cer

Steven Anderson · Jan 21, 2015 · Viewed 68.4k times · Source

I have the requirement to extract the public key (RSA) from a *.cer file. I wish to extract the key and store it in a .pem file so I can use its value to encrypt values using jsencrypt.

The following command converts a .cer to .pem:

openssl x509 -inform der -in certificate.cer -out certificate.pem

Yet it doesn't generate a file with the public key but a file with the contents of the *.cer file.

-----BEGIN CERTIFICATE-----
MIICPDCCAamgAwIBAg............
*lots of extra contents*
-----END CERTIFICATE-----

What command should I use to extract the public key and store it in a .pem file?

Answer

Using this command I was able to generate the .pem with the contents of the public key.

openssl x509 -inform der -in certificate.cer -pubkey -noout > certificate_publickey.pem

Which produces:

-----BEGIN PUBLIC KEY-----
MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQCsM+whXrxmbCkPfkwY2EehYpIp
*blah blah blah blah*
-----END PUBLIC KEY-----

How to extract the RSA public key from a .cer and store it in a .pem using OpenSSL?

Answer

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