pkcs1_to_x501.py

from M2Crypto import BIO, RSA 
import base64 

def der_length(length): 
    """DER encoding of a length""" 
    if length < 128: 
        return chr(length) 
    prefix = 0x80 
    result = '' 
    while length > 0: 
        result = chr(length & 0xff) + result 
        length >>= 8 
        prefix += 1 
    return chr(prefix) + result 
    
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 = '\0' + base64.decodestring("".join(pk[1:-2])) 
pk = '\x30\x0d\x06\x09\x2a\x86\x48\x86\xf7\x0d\x01\x01\x01\x05\x00\x03' + \ 
     der_length(len(pk)) + pk 
pk = '\x30' + der_length(len(pk)) + pk 
pk = '-----BEGIN PUBLIC KEY-----\n' + base64.encodestring(pk) + '-----END PUBLIC KEY-----' 

bio = BIO.MemoryBuffer(pk)