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cryptographyopensshpycryptoecdsa

Convert python cryptography EC key to OpenSSH format

I am looking to convert EC key generated using cryptography module to their respective OpenSSH strings. like

ecdsa-sha2-nistp256 AAAAE2VjZHNhLXNoYTItbmlzdHAyNTYAAAAhANiNlmyHtBUgaPXG+CtCVK8mQxBUtDjX3/nqqPZAHhduAAAAIE/JNDqLTeq9WVa5XWyU2Y7NJXfV54wakHmsP5gRNeh2

This is the code I use for EC key generation

from cryptography.hazmat.backends import default_backend
from cryptography.hazmat.primitives.asymmetric import ec
key=ec.generate_private_key(ec.SECP256R1(), default_backend())

I tried the following.

numbers = key.private_numbers()
opensshpublic = 'ecdsa-sha2-nistp256' + base64.b64encode('nistp256' + numbers.public_numbers.x, numbers.public_numbers.y)

but that didn't seem to work.

I suppose there should be a easy way to do this but I am missing something.

Solution

  • Cryptography added support for doing this in June 2016, it is possible as follows

    from cryptography.hazmat.primitives import serialization
key.public_bytes(serialization.Encoding.OpenSSH, serialization.PublicFormat.OpenSSH)

    this gives those neat OpenSSH public keys