diff options
Diffstat (limited to 'src/lib')
| -rw-r--r-- | src/lib/misc/fpe_fe1/fpe_fe1.cpp | 37 | ||||
| -rw-r--r-- | src/lib/misc/fpe_fe1/fpe_fe1.h | 33 |
2 files changed, 52 insertions, 18 deletions
diff --git a/src/lib/misc/fpe_fe1/fpe_fe1.cpp b/src/lib/misc/fpe_fe1/fpe_fe1.cpp index d06264413..0ec36363f 100644 --- a/src/lib/misc/fpe_fe1/fpe_fe1.cpp +++ b/src/lib/misc/fpe_fe1/fpe_fe1.cpp @@ -51,8 +51,6 @@ void factor(BigInt n, BigInt& a, BigInt& b) if(a > b) std::swap(a, b); a *= n; - if(a < b) - std::swap(a, b); if(a <= 1 || b <= 1) throw Exception("Could not factor n for use in FPE"); @@ -60,9 +58,15 @@ void factor(BigInt n, BigInt& a, BigInt& b) } -FPE_FE1::FPE_FE1(const BigInt& n, size_t rounds, const std::string& mac_algo) : +FPE_FE1::FPE_FE1(const BigInt& n, + size_t rounds, + bool compat_mode, + const std::string& mac_algo) : m_rounds(rounds) { + if(m_rounds < 3) + throw Invalid_Argument("FPE_FE1 rounds too small"); + m_mac = MessageAuthenticationCode::create_or_throw(mac_algo); m_n_bytes = BigInt::encode(n); @@ -72,19 +76,18 @@ FPE_FE1::FPE_FE1(const BigInt& n, size_t rounds, const std::string& mac_algo) : factor(n, m_a, m_b); - mod_a.reset(new Modular_Reducer(m_a)); - - /* - * According to a paper by Rogaway, Bellare, etc, the min safe number - * of rounds to use for FPE is 2+log_a(b). If a >= b then log_a(b) <= 1 - * so 3 rounds is safe. The FPE factorization routine should always - * return a >= b, so just confirm that and return 3. - */ - if(m_a < m_b) - throw Internal_Error("FPE rounds: a < b"); + if(compat_mode) + { + if(m_a < m_b) + std::swap(m_a, m_b); + } + else + { + if(m_a > m_b) + std::swap(m_a, m_b); + } - if(m_rounds < 3) - throw Invalid_Argument("FPE_FE1 rounds too small"); + mod_a.reset(new Modular_Reducer(m_a)); } FPE_FE1::~FPE_FE1() @@ -197,7 +200,7 @@ BigInt fe1_encrypt(const BigInt& n, const BigInt& X, const SymmetricKey& key, const std::vector<uint8_t>& tweak) { - FPE_FE1 fpe(n, 3, "HMAC(SHA-256)"); + FPE_FE1 fpe(n, 3, true, "HMAC(SHA-256)"); fpe.set_key(key); return fpe.encrypt(X, tweak.data(), tweak.size()); } @@ -206,7 +209,7 @@ BigInt fe1_decrypt(const BigInt& n, const BigInt& X, const SymmetricKey& key, const std::vector<uint8_t>& tweak) { - FPE_FE1 fpe(n, 3, "HMAC(SHA-256)"); + FPE_FE1 fpe(n, 3, true, "HMAC(SHA-256)"); fpe.set_key(key); return fpe.decrypt(X, tweak.data(), tweak.size()); } diff --git a/src/lib/misc/fpe_fe1/fpe_fe1.h b/src/lib/misc/fpe_fe1/fpe_fe1.h index 8f987fd65..e823a5d3c 100644 --- a/src/lib/misc/fpe_fe1/fpe_fe1.h +++ b/src/lib/misc/fpe_fe1/fpe_fe1.h @@ -16,11 +16,26 @@ 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 = 3, + size_t rounds = 5, + bool compat_mode = false, const std::string& mac_algo = "HMAC(SHA-256)"); ~FPE_FE1(); @@ -31,8 +46,18 @@ class BOTAN_PUBLIC_API(2,5) FPE_FE1 final : public SymmetricAlgorithm 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; @@ -67,6 +92,9 @@ namespace FPE { * @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, @@ -78,6 +106,9 @@ BigInt BOTAN_PUBLIC_API(2,0) fe1_encrypt(const BigInt& n, const BigInt& X, * @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, |