Read Base64 private key without encapsulation header in OpenSSL

Question

I am trying to decrypt a message using a private key with openssl. My implementation works fine when i use the private key in the following format

-----BEGIN RSA PRIVATE KEY-----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-----END RSA PRIVATE KEY-----

When I try with the same key without the encapsullation headers ( -----BEGIN RSA PRIVATE KEY----- and -----END RSA PRIVATE KEY----- ) it is failing.

Does these headers are mandatory for the keys?

If I want to use the key without headers which API of OpenSSL should i use?

Answer 1

The type of the key format is defined by the header and footer of the PEM encoded key. Internally it is just a PKCS#1 private key. For more information about the format you can look at this Q/A or the ASN.1 decoded key here .

So although all the information is in the base 64 encoding in the middle implementations may not directly be able to parse it, mainly because the type of the structure is not known.

You can however base 64 decode it and use it as a key within OpenSSL. You may need to specify -inform DER or something similar in that case.