Botan::ECIES_Decryptor Class Reference

#include <ecies.h>

Inheritance diagram for Botan::ECIES_Decryptor:

Public Member Functions
secure_vector< uint8_t >	decrypt (const uint8_t in[], size_t length) const
secure_vector< uint8_t >	decrypt (std::span< const uint8_t > in) const
secure_vector< uint8_t >	decrypt_or_random (const uint8_t in[], size_t length, size_t expected_pt_len, RandomNumberGenerator &rng) const
secure_vector< uint8_t >	decrypt_or_random (const uint8_t in[], size_t length, size_t expected_pt_len, RandomNumberGenerator &rng, const uint8_t required_content_bytes[], const uint8_t required_content_offsets[], size_t required_contents) const
	ECIES_Decryptor (const PK_Key_Agreement_Key &private_key, const ECIES_System_Params &ecies_params, RandomNumberGenerator &rng)
void	set_initialization_vector (const InitializationVector &iv)
	Set the initialization vector for the data encryption method.
void	set_label (std::string_view label)
	Set the label which is appended to the input for the message authentication code.

Detailed Description

ECIES Decryption according to ISO 18033-2

Definition at line 322 of file ecies.h.

Constructor & Destructor Documentation

ECIES_Decryptor()

Botan::ECIES_Decryptor::ECIES_Decryptor	(	const PK_Key_Agreement_Key &	private_key,
		const ECIES_System_Params &	ecies_params,
		RandomNumberGenerator &	rng )

Parameters

private_key	the private key which is used for the key agreement
ecies_params	settings for ecies
rng	the random generator to use

Definition at line 351 of file ecies.cpp.

                                                             :
      m_ka(key, ecies_params, false, rng), m_params(ecies_params) {
   /*
   ISO 18033: "If v > 1 and CheckMode = 0, then we must have gcd(u, v) = 1." (v = index, u= order)
 
   We skip this check because even if CheckMode = 0 we actually do check that
   the point is valid. In addition the check from ISO 18033 is pretty odd; u is
   the _prime_ order subgroup, and v is the cofactor. For gcd(u, v) > 1 to occur
   the cofactor would have to be a multiple of the group order, implying that
   the overall group was at least the square of the group order. Such a curve
   would also break our assumption that one can check for membership in the
   prime order subgroup by multiplying by the group order and checking for the
   identity.
   */
 
   m_mac = m_params.create_mac();
   m_cipher = m_params.create_cipher(Cipher_Dir::Decryption);
}

References Botan::Decryption.

Member Function Documentation

decrypt() [1/2]

secure_vector< uint8_t > Botan::PK_Decryptor::decrypt ( const uint8_t in[], size_t length ) const

inherited

Decrypt a ciphertext, throwing an exception if the input seems to be invalid (eg due to an accidental or malicious error in the ciphertext).

Parameters

in	the ciphertext as a byte array
length	the length of the above byte array

Returns

decrypted message

Definition at line 23 of file pubkey.cpp.

                                                                                    {
   uint8_t valid_mask = 0;
 
   secure_vector<uint8_t> decoded = do_decrypt(valid_mask, in, length);
 
   if(valid_mask == 0) {
      throw Decoding_Error("Invalid public key ciphertext, cannot decrypt");
   }
 
   return decoded;
}

Referenced by Botan::KeyPair::encryption_consistency_check().

decrypt() [2/2]

secure_vector< uint8_t > Botan::PK_Decryptor::decrypt ( std::span< const uint8_t > in ) const

inlineinherited

Same as above, but taking a vector

Parameters

in	the ciphertext

Returns

decrypted message

Definition at line 96 of file pubkey.h.

{ return decrypt(in.data(), in.size()); }

References decrypt().

Referenced by decrypt().

decrypt_or_random() [1/2]

secure_vector< uint8_t > Botan::PK_Decryptor::decrypt_or_random ( const uint8_t in[], size_t length, size_t expected_pt_len, RandomNumberGenerator & rng ) const

inherited

Decrypt a ciphertext. If the ciphertext is invalid (eg due to invalid padding) or is not the expected length, instead returns a random string of the expected length. Use to avoid oracle attacks, especially against PKCS #1 v1.5 decryption.

Definition at line 87 of file pubkey.cpp.

                                                                                         {
   return decrypt_or_random(in, length, expected_pt_len, rng, nullptr, nullptr, 0);
}

References decrypt_or_random().

Referenced by Botan::TLS::Client_Key_Exchange::Client_Key_Exchange(), and decrypt_or_random().

decrypt_or_random() [2/2]

secure_vector< uint8_t > Botan::PK_Decryptor::decrypt_or_random ( const uint8_t in[], size_t length, size_t expected_pt_len, RandomNumberGenerator & rng, const uint8_t required_content_bytes[], const uint8_t required_content_offsets[], size_t required_contents ) const

inherited

Decrypt a ciphertext. If the ciphertext is invalid (eg due to invalid padding) or is not the expected length, instead returns a random string of the expected length. Use to avoid oracle attacks, especially against PKCS #1 v1.5 decryption.

Additionally checks (also in const time) that: contents[required_content_offsets[i]] == required_content_bytes[i] for 0 <= i < required_contents

Used for example in TLS, which encodes the client version in the content bytes: if there is any timing variation the version check can be used as an oracle to recover the key.

Definition at line 35 of file pubkey.cpp.

                                                                                              {
   const secure_vector<uint8_t> fake_pms = [&]() {
      auto pms = rng.random_vec(expected_pt_len);
 
      for(size_t i = 0; i != required_contents_length; ++i) {
         const uint8_t exp = required_content_bytes[i];
 
         /*
         If an offset repeats we don't detect this and just return a PMS that satisfies
         the last requested index. If the requested (idx,value) tuple is the same, that's
         fine and just redundant. If they disagree, decryption will always fail, since the
         same byte cannot possibly have two distinct values.
         */
         const uint8_t off = required_content_offsets[i];
         BOTAN_ASSERT(off < expected_pt_len, "Offset in range of plaintext");
         pms[off] = exp;
      }
 
      return pms;
   }();
 
   uint8_t decrypt_valid = 0;
   secure_vector<uint8_t> decoded = do_decrypt(decrypt_valid, in, length);
 
   auto valid_mask = CT::Mask<uint8_t>::is_equal(decrypt_valid, 0xFF);
   valid_mask &= CT::Mask<uint8_t>(CT::Mask<size_t>::is_equal(decoded.size(), expected_pt_len));
 
   decoded.resize(expected_pt_len);
 
   for(size_t i = 0; i != required_contents_length; ++i) {
      const uint8_t exp = required_content_bytes[i];
 
      // We know off is in range because we already checked it when creating the fake premaster above
      const uint8_t off = required_content_offsets[i];
 
      auto eq = CT::Mask<uint8_t>::is_equal(decoded[off], exp);
 
      valid_mask &= eq;
   }
 
   // If valid_mask is false, assign fake pre master instead
   valid_mask.select_n(decoded.data(), decoded.data(), fake_pms.data(), expected_pt_len);
 
   return decoded;
}

References BOTAN_ASSERT, Botan::CT::Mask< T >::is_equal(), and Botan::RandomNumberGenerator::random_vec().

set_initialization_vector()

void Botan::ECIES_Decryptor::set_initialization_vector ( const InitializationVector & iv )

inline

Set the initialization vector for the data encryption method.

Definition at line 334 of file ecies.h.

{ m_iv = iv; }

set_label()

void Botan::ECIES_Decryptor::set_label ( std::string_view label )

inline

Set the label which is appended to the input for the message authentication code.

Definition at line 337 of file ecies.h.

{ m_label = std::vector<uint8_t>(label.begin(), label.end()); }

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The documentation for this class was generated from the following files:

• src/lib/pubkey/ecies/ecies.h
• src/lib/pubkey/ecies/ecies.cpp