SSH Public-Private Key Format

Updated 13 Sep 2026

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What it is
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  SSH stores private keys in PEM format (-----BEGIN RSA PRIVATE KEY-----, etc.). Public keys, however, use SSH's own single-line wire format instead: ssh-rsa <base64-encoded-key-blob> comment, designed to be easy to append as a line in a server's ~/.ssh/authorized_keys.
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When to apply
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  A file starting with ssh-rsa, ssh-ed25519, etc. (a .pub file) needs to be converted before standard crypto libraries like PyCryptodome can parse it.
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Worked example
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  ssh-keygen -f id_rsa.pub -e -m pem > id_rsa.pem turns the one-line ssh-rsa AAAA... format into a standard PEM block that RSA.import_key() can read directly.

Python

from Crypto.PublicKey import RSA
# after: ssh-keygen -f key.pub -e -m pem > key.pem
key = RSA.import_key(open("key.pem").read())
print(key.n)