How to read a RSA public key in PEM + PKCS#1 format

Question

I have a RSA public key in PEM format + PKCS#1(I guess):

-----BEGIN RSA PUBLIC KEY----- MIGJAoGBAJNrHWRFgWLqgzSmLBq2G89exgi/Jk1NWhbFB9gHc9MLORmP3BOCJS9k onzT/+Dk1hdZf00JGgZeuJGoXK9PX3CIKQKRQRHpi5e1vmOCrmHN5VMOxGO4d+zn JDEbNHODZR4HzsSdpQ9SGMSx7raJJedEIbr0IP6DgnWgiA7R1mUdAgMBAAE= -----END RSA PUBLIC KEY----- 

I want to get the SHA1 digest of its ASN1 encoded version in Python. The first step should be to read this key, but I failed to do it in PyCrypto:

>> from Crypto.PublicKey import RSA >> RSA.importKey(my_key) ValueError: RSA key format is not supported 

The documentation of PyCrypto says PEM + PKCS#1 is supported, so I'm confused. I've also tried M2Crypto, but it turns out that M2Crypto does not support PKCS#1 but only X.509.

Answer 1

PyCrypto supports PKCS#1 in the sense that it can read in X.509 SubjectPublicKeyInfo objects that contain an RSA public key encoded in PKCS#1.

Instead, the data encoded in your key is a pure RSAPublicKey object (that is, an ASN.1 SEQUENCE with two INTEGERs, modulus and public exponent).

You can still read it in though. Try something like:

from Crypto.PublicKey import RSA from Crypto.Util import asn1 from base64 import b64decode  key64 = 'MIGJAoGBAJNrHWRFgWLqgzSmLBq2G89exgi/Jk1NWhbFB9gHc9MLORmP3BOCJS9k\ onzT/+Dk1hdZf00JGgZeuJGoXK9PX3CIKQKRQRHpi5e1vmOCrmHN5VMOxGO4d+znJDEbNHOD\ ZR4HzsSdpQ9SGMSx7raJJedEIbr0IP6DgnWgiA7R1mUdAgMBAAE='  keyDER = b64decode(key64) seq = asn1.DerSequence() seq.decode(keyDER) keyPub = RSA.construct( (seq[0], seq[1]) ) 

---

Starting from version 2.6, PyCrypto can import also RsaPublicKey ASN.1 objects. The code is then much simpler:

from Crypto.PublicKey import RSA from base64 import b64decode  key64 = b'MIGJAoGBAJNrHWRFgWLqgzSmLBq2G89exgi/Jk1NWhbFB9gHc9MLORmP3BOCJS9k\ onzT/+Dk1hdZf00JGgZeuJGoXK9PX3CIKQKRQRHpi5e1vmOCrmHN5VMOxGO4d+znJDEbNHOD\ ZR4HzsSdpQ9SGMSx7raJJedEIbr0IP6DgnWgiA7R1mUdAgMBAAE='  keyDER = b64decode(key64) keyPub = RSA.importKey(keyDER)