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/*
* Format Preserving Encryption (FE1 scheme)
* (C) 2009,2018 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
#ifndef BOTAN_FPE_FE1_H_
#define BOTAN_FPE_FE1_H_
#include <botan/sym_algo.h>
#include <botan/bigint.h>
namespace Botan {
class Modular_Reducer;
class MessageAuthenticationCode;
/**
* Format Preserving Encryption using the scheme FE1 from the paper
* "Format-Preserving Encryption" by Bellare, Rogaway, et al
* (https://eprint.iacr.org/2009/251)
*/
class BOTAN_PUBLIC_API(2,5) FPE_FE1 final : public SymmetricAlgorithm
{
public:
/**
* @param n the modulus. All plaintext and ciphertext values must be
* less than this.
* @param rounds the number of rounds to use. Must be at least 3.
* @param compat_mode An error in versions before 2.5.0 chose incorrect
* values for a and b. Set compat_mode to true to select this version.
* @param mac_algo the PRF to use as the encryption function
*/
FPE_FE1(const BigInt& n,
size_t rounds = 5,
bool compat_mode = false,
const std::string& mac_algo = "HMAC(SHA-256)");
~FPE_FE1();
Key_Length_Specification key_spec() const override;
std::string name() const override;
void clear() override;
/**
* Encrypt X from and onto the group Z_n using key and tweak
* @param x the plaintext to encrypt <= n
* @param tweak will modify the ciphertext
*/
BigInt encrypt(const BigInt& x, const uint8_t tweak[], size_t tweak_len) const;
/**
* Decrypt X from and onto the group Z_n using key and tweak
* @param x the ciphertext to encrypt <= n
* @param tweak must match the value used to encrypt
*/
BigInt decrypt(const BigInt& x, const uint8_t tweak[], size_t tweak_len) const;
BigInt encrypt(const BigInt& x, uint64_t tweak) const;
BigInt decrypt(const BigInt& x, uint64_t tweak) const;
private:
void key_schedule(const uint8_t key[], size_t length) override;
BigInt F(const BigInt& R, size_t round,
const secure_vector<uint8_t>& tweak,
secure_vector<uint8_t>& tmp) const;
secure_vector<uint8_t> compute_tweak_mac(const uint8_t tweak[], size_t tweak_len) const;
std::unique_ptr<MessageAuthenticationCode> m_mac;
std::unique_ptr<Modular_Reducer> mod_a;
std::vector<uint8_t> m_n_bytes;
BigInt m_a;
BigInt m_b;
size_t m_rounds;
};
namespace FPE {
/**
* Format Preserving Encryption using the scheme FE1 from the paper
* "Format-Preserving Encryption" by Bellare, Rogaway, et al
* (https://eprint.iacr.org/2009/251)
*
* Encrypt X from and onto the group Z_n using key and tweak
* @param n the modulus
* @param X the plaintext as a BigInt
* @param key a random key
* @param tweak will modify the ciphertext (think of as an IV)
*
* @warning This function is hardcoded to use only 3 rounds which
* may be insecure for some values of n. Prefer FPE_FE1 class
*/
BigInt BOTAN_PUBLIC_API(2,0) fe1_encrypt(const BigInt& n, const BigInt& X,
const SymmetricKey& key,
const std::vector<uint8_t>& tweak);
/**
* Decrypt X from and onto the group Z_n using key and tweak
* @param n the modulus
* @param X the ciphertext as a BigInt
* @param key is the key used for encryption
* @param tweak the same tweak used for encryption
*
* @warning This function is hardcoded to use only 3 rounds which
* may be insecure for some values of n. Prefer FPE_FE1 class
*/
BigInt BOTAN_PUBLIC_API(2,0) fe1_decrypt(const BigInt& n, const BigInt& X,
const SymmetricKey& key,
const std::vector<uint8_t>& tweak);
}
}
#endif
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