Loading a PKCS#1 public key using M2Crypto

[Piet van Oostrum]

Marc Aymerich <glicerinu at gmail.com> writes:

> Hi, 
> I've been trying very, very hard to load an RSA key using M2Crypto but without any success.
>
> basically this is what I'm trying to do:
>>>> from M2Crypto import BIO, RSA
>>>> 
>>>> pubkey = """-----BEGIN RSA PUBLIC KEY-----
> ... MIIBCgKCAQEApwotnfHT9RAmxnuaGEMdI3lYPYE4aaqSD9v4KbTh1E7Le3GNJQb7
> ... wCpmDe8+n8S5Kp/gBEpWiYuvsVA/T4KseoX7NMcacP+DJMwjmNd9U58USn2vLz0Z
> ... TMtXpc/FUhW5PZdgCiuNzw6IFgGn9ZCCv85jjUIW3KD8fUNdrUfVSv4olDoL9NkR
> ... dTRg3Os/znC6l0gv/mqnLaqj2bJ/tx47kUmj6Oq13JuEq34T+DVmsUCFVundQnRp
> ... c/vVEqQot7Rvj9UmSvTi4WKt/qxiAnyZf3gXOdrXvxfVTGzD5I/Xg+By+a4C2JwB
> ... A5RGvZP3fyfhkCnnhFDpfws5lc20FA6ryQIDAQAB
> ... -----END RSA PUBLIC KEY-----"""
>>>> 
>>>> bio = BIO.MemoryBuffer(pubkey.encode('ascii'))
>>>> RSA.load_pub_key_bio(bio)
> Traceback (most recent call last):
>   File "<stdin>", line 1, in <module>
>   File "/usr/lib/python2.7/dist-packages/M2Crypto/RSA.py", line 422, in load_pub_key_bio
>     rsa_error()
>   File "/usr/lib/python2.7/dist-packages/M2Crypto/RSA.py", line 302, in rsa_error
>     raise RSAError, m2.err_reason_error_string(m2.err_get_error())
> M2Crypto.RSA.RSAError: no start line
>
>
> Reading all whats in Internet about this problem it seems that my key is in PKCS#1 format but M2Crypto only reads X.501 RSA keys. 
>
> I know that python-crypto doesn't have any problem loading this key, but I'll prefer to stick with M2Crypto because I already have lots code using M2Crypto.
>
> So my question is, is there any way to load this key using M2Crypto? Can I convert somehow the key to X.501?
>
Converting to X.501 isn't difficult (assuming this is a 2048 bit key):
Get rid of the 'RSA' in header and trailer
Prepend X.501 header 'MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8A' to the data
Reformat the lines to 64 characters.

from M2Crypto import BIO, RSA

pubkey="""-----BEGIN RSA PUBLIC KEY-----
MIIBCgKCAQEApwotnfHT9RAmxnuaGEMdI3lYPYE4aaqSD9v4KbTh1E7Le3GNJQb7
wCpmDe8+n8S5Kp/gBEpWiYuvsVA/T4KseoX7NMcacP+DJMwjmNd9U58USn2vLz0Z
TMtXpc/FUhW5PZdgCiuNzw6IFgGn9ZCCv85jjUIW3KD8fUNdrUfVSv4olDoL9NkR
dTRg3Os/znC6l0gv/mqnLaqj2bJ/tx47kUmj6Oq13JuEq34T+DVmsUCFVundQnRp
c/vVEqQot7Rvj9UmSvTi4WKt/qxiAnyZf3gXOdrXvxfVTGzD5I/Xg+By+a4C2JwB
A5RGvZP3fyfhkCnnhFDpfws5lc20FA6ryQIDAQAB
-----END RSA PUBLIC KEY-----
"""

pk = pubkey.split('\n')
pk = 'MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8A' + ''.join(pk[1:-2])
pk = [pk[i:i+64] for i in range(0, len(pk), 64)]
pk = '-----BEGIN PUBLIC KEY-----\n' + '\n'.join(pk) + '\n-----END PUBLIC KEY-----'

bio = BIO.MemoryBuffer(pk) # pk is ASCII, don't encode
key = RSA.load_pub_key_bio(bio)

-- 
Piet van Oostrum <piet at vanoostrum.org>
WWW: http://pietvanoostrum.com/
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