Botan::FPE Namespace Reference

Functions
BigInt	fe1_decrypt (const BigInt &n, const BigInt &X0, const SymmetricKey &key, const MemoryRegion< byte > &tweak)
BigInt	fe1_encrypt (const BigInt &n, const BigInt &X0, const SymmetricKey &key, const MemoryRegion< byte > &tweak)

Function Documentation

fe1_decrypt()

BigInt BOTAN_DLL Botan::FPE::fe1_decrypt	(	const BigInt &	n,
		const BigInt &	X,
		const SymmetricKey &	key,
		const MemoryRegion< byte > &	tweak )

Decrypt X from and onto the group Z_n using key and tweak

Parameters

n	the modulus
X	the ciphertext as a BigInt
key	is the key used for encryption
tweak	the same tweak used for encryption

Definition at line 166 of file fpe_fe1.cpp.

   {
   FPE_Encryptor F(key, n, tweak);
 
   BigInt a, b;
   factor(n, a, b);
 
   const size_t r = rounds(a, b);
 
   BigInt X = X0;
 
   for(size_t i = 0; i != r; ++i)
      {
      BigInt W = X % a;
      BigInt R = X / a;
 
      BigInt L = (W - F(r-i-1, R)) % a;
      X = b * L + R;
      }
 
   return X;
   }

References fe1_decrypt().

Referenced by fe1_decrypt().

fe1_encrypt()

BigInt BOTAN_DLL Botan::FPE::fe1_encrypt	(	const BigInt &	n,
		const BigInt &	X,
		const SymmetricKey &	key,
		const MemoryRegion< byte > &	tweak )

Encrypt X from and onto the group Z_n using key and tweak

Parameters

n	the modulus
X	the plaintext as a BigInt
key	a random key
tweak	will modify the ciphertext (think of as an IV)

Definition at line 138 of file fpe_fe1.cpp.

   {
   FPE_Encryptor F(key, n, tweak);
 
   BigInt a, b;
   factor(n, a, b);
 
   const size_t r = rounds(a, b);
 
   BigInt X = X0;
 
   for(size_t i = 0; i != r; ++i)
      {
      BigInt L = X / b;
      BigInt R = X % b;
 
      BigInt W = (L + F(i, R)) % a;
      X = a * R + W;
      }
 
   return X;
   }

References fe1_encrypt().

Referenced by fe1_encrypt().