from M2Crypto import EC, EVP
import binascii, sys, cryptimage
from pydmtx import DataMatrix
debug=0
ecpubkey = binascii.a2b_hex('02b6fd5e085b9aa66de4bb501d4ede5e2b5215680cc7d8c050aab7a8dc505213c1')
ecder = cryptimage.build_asn1(ecpubkey)
ecpub = EC.pub_key_from_der(ecder)
digest = EVP.MessageDigest("sha1")
digest.update(cryptimage.compress_key(ecpubkey))
fingerprint = digest.digest()
# NID_X9_62_prime256v1
ephemeral = EC.gen_params(EC.NID_X9_62_prime256v1)
ephemeral.gen_key()
ephpub=cryptimage.strip_asn1(ephemeral.pub().get_der())
ephpub=cryptimage.compress_key(ephpub)
shared = ephemeral.compute_dh_key(ecpub.pub())
#strip second half of key which is y cordinates and can be derived from first half
dk=cryptimage.KDF(shared[:len(shared)/2],128,fingerprint)
if debug: sys.stderr.write("dk = %s\n" % binascii.b2a_hex(dk))
account="2000111122223333"
amount="1500050"
pin="7654"
data=cryptimage.dataencode(account,amount,pin)
if debug: sys.stderr.write("ct = %s\n" % binascii.b2a_hex(ciphertext))
ecpairpem = """-----BEGIN EC PRIVATE KEY-----
MHcCAQEEIH8TNBOfV+JWVBr25KfjJ1007paZ/JnrvjxFzZThUgSToAoGCCqGSM49
AwEHoUQDQgAEtv1eCFuapm3ku1AdTt5eK1IVaAzH2MBQqreo3FBSE8EHxCsEGRvK
auFV+AgDEQotZbdqzAojRoCjuhZcYP73Pg==
-----END EC PRIVATE KEY-----
"""
#derive shared key
ecbio = BIO.MemoryBuffer()
ecbio.write(ecpairpem)
ecpair = EC.load_key_bio(ecbio)
ecder = ecpair.pub().get_der()
ecpub = cryptimage.compress_key(cryptimage.strip_asn1(ecder))
digest = EVP.MessageDigest("sha1")
digest.update(ecpub)
fingerprint = digest.digest()
shared = ecpair.compute_dh_key(ephemeral.pub())
dk=cryptimage.KDF(shared[:len(shared)/2],128,fingerprint)
#decrypt message, extract contents and print results
plaintext = cryptimage.decrypt_data(dk,ciphertext)
[account,amount,pin]=cryptimage.datadecode(plaintext)
print "Destination account number is: " + account
print "Amount to be transfered: %.2f" % (float(amount)/100)
print "Please enter pin %s to verify transaction" % pin