RSA key parameters in pyOpenSSL from P12

Question

I'm using pyOpenSSL and I have a PKCS12 object and with the get_privateKey() and get_publicKey() methods one can obtain the RSA Private/Public key objects. Is there a way from these objects to extract the RSA key parameters (p, q, dp, dq, qinv)?

Answer 1

You can use ASN1 parser to get the key parameters:

from OpenSSL.crypto import dump_privatekey, FILETYPE_ASN1
from Crypto.Util.asn1 import DerSequence

private_key_der = DerSequence()
# private_key is obtained from PKCS12 object using get_privateKey()
private_key_der.decode(dump_privatekey(FILETYPE_ASN1, private_key))

The private_key_der will contain the key parameters according to the following der structure

RSAPrivateKey ::= SEQUENCE {
  version           Version,
  modulus           INTEGER,  -- n
  publicExponent    INTEGER,  -- e
  privateExponent   INTEGER,  -- d
  prime1            INTEGER,  -- p
  prime2            INTEGER,  -- q
  exponent1         INTEGER,  -- d mod (p-1)
  exponent2         INTEGER,  -- d mod (q-1)
  coefficient       INTEGER,  -- (inverse of q) mod p
  otherPrimeInfos   OtherPrimeInfos OPTIONAL
}

which in python will be equivalent to:

private_key_der[0] # version
private_key_der[1] # modulus
private_key_der[2] # publicExponent
private_key_der[3] # privateExponent
private_key_der[4] # prime1
private_key_der[5] # prime2
private_key_der[6] # exponent1
private_key_der[7] # exponent2
private_key_der[8] # coefficient
private_key_der[9] # otherPrimeInfos