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Diffstat (limited to 'examples/fpe.cpp')
-rw-r--r-- | examples/fpe.cpp | 151 |
1 files changed, 151 insertions, 0 deletions
diff --git a/examples/fpe.cpp b/examples/fpe.cpp new file mode 100644 index 000000000..9b18d4879 --- /dev/null +++ b/examples/fpe.cpp @@ -0,0 +1,151 @@ +/* +* (C) 2009 Jack Lloyd +* +* Distributed under the terms of the Botan license +*/ + +/* +* Encrypt credit cards numbers with valid checksums into other credit +* card numbers with valid checksums using format preserving encryption. +*/ + +#include <botan/fpe.h> +#include <botan/sha160.h> +#include <botan/init.h> + +using namespace Botan; + +#include <iostream> +#include <stdexcept> + +namespace { + +byte luhn_checksum(u64bit cc_number) + { + byte sum = 0; + + bool alt = false; + while(cc_number) + { + byte digit = cc_number % 10; + if(alt) + { + digit *= 2; + if(digit > 9) + digit -= 9; + } + + sum += digit; + + cc_number /= 10; + alt = !alt; + } + + return (sum % 10); + } + +bool luhn_check(u64bit cc_number) + { + return (luhn_checksum(cc_number) == 0); + } + +u64bit cc_rank(u64bit cc_number) + { + // Remove Luhn checksum + return cc_number / 10; + } + +u64bit cc_derank(u64bit cc_number) + { + for(u32bit i = 0; i != 10; ++i) + if(luhn_check(cc_number * 10 + i)) + return (cc_number * 10 + i); + return 0; + } + +/* +* Use the SHA-1 hash of the account name or ID as a tweak +*/ +SecureVector<byte> sha1(const std::string& acct_name) + { + SHA_160 hash; + hash.update(acct_name); + return hash.final(); + } + +u64bit encrypt_cc_number(u64bit cc_number, + const SymmetricKey& key, + const std::string& acct_name) + { + BigInt n = 1000000000000000; + + u64bit cc_ranked = cc_rank(cc_number); + + BigInt c = fpe_encrypt(n, cc_ranked, key, sha1(acct_name)); + + if(c.bits() > 50) + throw std::runtime_error("FPE produced a number too large"); + + u64bit enc_cc = 0; + for(u32bit i = 0; i != 7; ++i) + enc_cc = (enc_cc << 8) | c.byte_at(6-i); + return cc_derank(enc_cc); + } + +u64bit decrypt_cc_number(u64bit enc_cc, + const SymmetricKey& key, + const std::string& acct_name) + { + BigInt n = 1000000000000000; + + u64bit cc_ranked = cc_rank(enc_cc); + + BigInt c = fpe_decrypt(n, cc_ranked, key, sha1(acct_name)); + + if(c.bits() > 50) + throw std::runtime_error("FPE produced a number too large"); + + u64bit dec_cc = 0; + for(u32bit i = 0; i != 7; ++i) + dec_cc = (dec_cc << 8) | c.byte_at(6-i); + return cc_derank(dec_cc); + } + +} + +int main(int argc, char* argv[]) + { + LibraryInitializer init; + + if(argc != 4) + { + std::cout << "Usage: " << argv[0] << " cc-number acct-name passwd\n"; + return 1; + } + + u64bit cc_number = atoll(argv[1]); + std::string acct_name = argv[2]; + std::string passwd = argv[3]; + + std::cout << "Input was: " << cc_number << ' ' + << luhn_check(cc_number) << '\n'; + + /** + * In practice something like PBKDF2 with a salt and high iteration + * count would be a good idea. + */ + SymmetricKey key = sha1(passwd); + + u64bit enc_cc = encrypt_cc_number(cc_number, key, acct_name); + + std::cout << "Encrypted: " << enc_cc + << ' ' << luhn_check(enc_cc) << '\n'; + + u64bit dec_cc = decrypt_cc_number(enc_cc, key, acct_name); + + std::cout << "Decrypted: " << dec_cc + << ' ' << luhn_check(dec_cc) << '\n'; + + if(dec_cc != cc_number) + std::cout << "Something went wrong :( Bad CC checksum?\n"; + } |