PyBitmessage/src/highlevelcrypto.py

from binascii import hexlify
from bmconfigparser import BMConfigParser
import pyelliptic
from pyelliptic import arithmetic as a, OpenSSL
def makeCryptor(privkey):
    private_key = a.changebase(privkey, 16, 256, minlen=32)
    public_key = pointMult(private_key)
    privkey_bin = '\x02\xca\x00\x20' + private_key
    pubkey_bin = '\x02\xca\x00\x20' + public_key[1:-32] + '\x00\x20' + public_key[-32:]
    cryptor = pyelliptic.ECC(curve='secp256k1',privkey=privkey_bin,pubkey=pubkey_bin)
    return cryptor
def hexToPubkey(pubkey):
    pubkey_raw = a.changebase(pubkey[2:],16,256,minlen=64)
    pubkey_bin = '\x02\xca\x00 '+pubkey_raw[:32]+'\x00 '+pubkey_raw[32:]
    return pubkey_bin
def makePubCryptor(pubkey):
    pubkey_bin = hexToPubkey(pubkey)
    return pyelliptic.ECC(curve='secp256k1',pubkey=pubkey_bin)
# Converts hex private key into hex public key
def privToPub(privkey):
    private_key = a.changebase(privkey, 16, 256, minlen=32)
    public_key = pointMult(private_key)
    return hexlify(public_key)
# Encrypts message with hex public key
def encrypt(msg,hexPubkey):
    return pyelliptic.ECC(curve='secp256k1').encrypt(msg,hexToPubkey(hexPubkey))
# Decrypts message with hex private key
def decrypt(msg,hexPrivkey):
    return makeCryptor(hexPrivkey).decrypt(msg)
# Decrypts message with an existing pyelliptic.ECC.ECC object
def decryptFast(msg,cryptor):
    return cryptor.decrypt(msg)
# Signs with hex private key
def sign(msg,hexPrivkey):
    # pyelliptic is upgrading from SHA1 to SHA256 for signing. We must 
    # upgrade PyBitmessage gracefully. 
    # https://github.com/yann2192/pyelliptic/pull/33
    # More discussion: https://github.com/yann2192/pyelliptic/issues/32
    digestAlg = BMConfigParser().safeGet('bitmessagesettings', 'digestalg', 'sha1')
    if digestAlg == "sha1":
        # SHA1, this will eventually be deprecated
        return makeCryptor(hexPrivkey).sign(msg, digest_alg=OpenSSL.digest_ecdsa_sha1)
    elif digestAlg == "sha256":
        # SHA256. Eventually this will become the default
        return makeCryptor(hexPrivkey).sign(msg, digest_alg=OpenSSL.EVP_sha256)
    else:
        raise ValueError("Unknown digest algorithm %s" % (digestAlg))
# Verifies with hex public key
def verify(msg,sig,hexPubkey):
    # As mentioned above, we must upgrade gracefully to use SHA256. So
    # let us check the signature using both SHA1 and SHA256 and if one
    # of them passes then we will be satisfied. Eventually this can 
    # be simplified and we'll only check with SHA256. 
    try:
        sigVerifyPassed = makePubCryptor(hexPubkey).verify(sig,msg,digest_alg=OpenSSL.digest_ecdsa_sha1) # old SHA1 algorithm.
    except:
        sigVerifyPassed = False
    if sigVerifyPassed:
        # The signature check passed using SHA1
        return True
    # The signature check using SHA1 failed. Let us try it with SHA256. 
    try:
        return makePubCryptor(hexPubkey).verify(sig,msg,digest_alg=OpenSSL.EVP_sha256)
    except:
        return False

# Does an EC point multiplication; turns a private key into a public key.
def pointMult(secret):
    while True:
        try:
            """
            Evidently, this type of error can occur very rarely:
            
            File "highlevelcrypto.py", line 54, in pointMult
              group = OpenSSL.EC_KEY_get0_group(k)
            WindowsError: exception: access violation reading 0x0000000000000008
            """
            k = OpenSSL.EC_KEY_new_by_curve_name(OpenSSL.get_curve('secp256k1'))
            priv_key = OpenSSL.BN_bin2bn(secret, 32, None)
            group = OpenSSL.EC_KEY_get0_group(k)
            pub_key = OpenSSL.EC_POINT_new(group)
            
            OpenSSL.EC_POINT_mul(group, pub_key, priv_key, None, None, None)
            OpenSSL.EC_KEY_set_private_key(k, priv_key)
            OpenSSL.EC_KEY_set_public_key(k, pub_key)
            
            size = OpenSSL.i2o_ECPublicKey(k, None)
            mb = OpenSSL.create_string_buffer(size)
            OpenSSL.i2o_ECPublicKey(k, OpenSSL.byref(OpenSSL.pointer(mb)))
            
            OpenSSL.EC_POINT_free(pub_key)
            OpenSSL.BN_free(priv_key)
            OpenSSL.EC_KEY_free(k)
            return mb.raw

        except Exception as e:
            import traceback
            import time
            traceback.print_exc()
            time.sleep(0.2)