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#include "examples.h"
#include <botan/fpe_fe1.h>
#include <botan/sha160.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
*/
std::vector<byte> sha1(const std::string& acct_name)
{
SHA_160 hash;
hash.update(acct_name);
return unlock(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::fe1_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::fe1_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 fpe_example(int argc, char* argv[])
{
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";
return 2;
}
return 0;
}
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