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/*
* DLIES
* (C) 1999-2007 Jack Lloyd
* (C) 2016 Daniel Neus, Rohde & Schwarz Cybersecurity
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
#include <botan/dlies.h>
#include <botan/internal/ct_utils.h>
#include <limits>
namespace Botan {
DLIES_Encryptor::DLIES_Encryptor(const DH_PrivateKey& own_priv_key,
RandomNumberGenerator& rng,
KDF* kdf,
MessageAuthenticationCode* mac,
size_t mac_key_length) :
DLIES_Encryptor(own_priv_key, rng, kdf, nullptr, 0, mac, mac_key_length)
{
}
DLIES_Encryptor::DLIES_Encryptor(const DH_PrivateKey& own_priv_key,
RandomNumberGenerator& rng,
KDF* kdf,
Cipher_Mode* cipher,
size_t cipher_key_len,
MessageAuthenticationCode* mac,
size_t mac_key_length) :
m_other_pub_key(),
m_own_pub_key(own_priv_key.public_value()),
m_ka(own_priv_key, rng, "Raw"),
m_kdf(kdf),
m_cipher(cipher),
m_cipher_key_len(cipher_key_len),
m_mac(mac),
m_mac_keylen(mac_key_length),
m_iv()
{
BOTAN_ASSERT_NONNULL(kdf);
BOTAN_ASSERT_NONNULL(mac);
}
std::vector<uint8_t> DLIES_Encryptor::enc(const uint8_t in[], size_t length,
RandomNumberGenerator&) const
{
if(m_other_pub_key.empty())
{
throw Invalid_State("DLIES: The other key was never set");
}
// calculate secret value
const SymmetricKey secret_value = m_ka.derive_key(0, m_other_pub_key);
// derive secret key from secret value
const size_t required_key_length = m_cipher ? m_cipher_key_len + m_mac_keylen : length + m_mac_keylen;
const secure_vector<uint8_t> secret_keys = m_kdf->derive_key(required_key_length, secret_value.bits_of());
if(secret_keys.size() != required_key_length)
{
throw Encoding_Error("DLIES: KDF did not provide sufficient output");
}
secure_vector<uint8_t> ciphertext(in, in + length);
const size_t cipher_key_len = m_cipher ? m_cipher_key_len : length;
if(m_cipher)
{
SymmetricKey enc_key(secret_keys.data(), cipher_key_len);
m_cipher->set_key(enc_key);
if(m_iv.size())
{
m_cipher->start(m_iv.bits_of());
}
m_cipher->finish(ciphertext);
}
else
{
xor_buf(ciphertext, secret_keys, cipher_key_len);
}
// calculate MAC
m_mac->set_key(secret_keys.data() + cipher_key_len, m_mac_keylen);
secure_vector<uint8_t> tag = m_mac->process(ciphertext);
// out = (ephemeral) public key + ciphertext + tag
secure_vector<uint8_t> out(m_own_pub_key.size() + ciphertext.size() + tag.size());
buffer_insert(out, 0, m_own_pub_key);
buffer_insert(out, 0 + m_own_pub_key.size(), ciphertext);
buffer_insert(out, 0 + m_own_pub_key.size() + ciphertext.size(), tag);
return unlock(out);
}
/**
* Return the max size, in bytes, of a message
* We assume DLIES is only used for key transport and limit the maximum size
* to 512 bits
*/
size_t DLIES_Encryptor::maximum_input_size() const
{
return 64;
}
size_t DLIES_Encryptor::ciphertext_length(size_t ptext_len) const
{
return m_own_pub_key.size() + m_mac->output_length() + m_cipher->output_length(ptext_len);
}
DLIES_Decryptor::DLIES_Decryptor(const DH_PrivateKey& own_priv_key,
RandomNumberGenerator& rng,
KDF* kdf,
Cipher_Mode* cipher,
size_t cipher_key_len,
MessageAuthenticationCode* mac,
size_t mac_key_length) :
m_pub_key_size(own_priv_key.public_value().size()),
m_ka(own_priv_key, rng, "Raw"),
m_kdf(kdf),
m_cipher(cipher),
m_cipher_key_len(cipher_key_len),
m_mac(mac),
m_mac_keylen(mac_key_length),
m_iv()
{
BOTAN_ASSERT_NONNULL(kdf);
BOTAN_ASSERT_NONNULL(mac);
}
DLIES_Decryptor::DLIES_Decryptor(const DH_PrivateKey& own_priv_key,
RandomNumberGenerator& rng,
KDF* kdf,
MessageAuthenticationCode* mac,
size_t mac_key_length) :
DLIES_Decryptor(own_priv_key, rng, kdf, nullptr, 0, mac, mac_key_length)
{}
size_t DLIES_Decryptor::plaintext_length(size_t ctext_len) const
{
if(ctext_len < m_pub_key_size + m_mac->output_length())
return 0; // will throw if attempted
return ctext_len - (m_pub_key_size + m_mac->output_length());
}
secure_vector<uint8_t> DLIES_Decryptor::do_decrypt(uint8_t& valid_mask,
const uint8_t msg[], size_t length) const
{
if(length < m_pub_key_size + m_mac->output_length())
{
throw Decoding_Error("DLIES decryption: ciphertext is too short");
}
// calculate secret value
std::vector<uint8_t> other_pub_key(msg, msg + m_pub_key_size);
const SymmetricKey secret_value = m_ka.derive_key(0, other_pub_key);
const size_t ciphertext_len = length - m_pub_key_size - m_mac->output_length();
size_t cipher_key_len = m_cipher ? m_cipher_key_len : ciphertext_len;
// derive secret key from secret value
const size_t required_key_length = cipher_key_len + m_mac_keylen;
secure_vector<uint8_t> secret_keys = m_kdf->derive_key(required_key_length, secret_value.bits_of());
if(secret_keys.size() != required_key_length)
{
throw Encoding_Error("DLIES: KDF did not provide sufficient output");
}
secure_vector<uint8_t> ciphertext(msg + m_pub_key_size, msg + m_pub_key_size + ciphertext_len);
// calculate MAC
m_mac->set_key(secret_keys.data() + cipher_key_len, m_mac_keylen);
secure_vector<uint8_t> calculated_tag = m_mac->process(ciphertext);
// calculated tag == received tag ?
secure_vector<uint8_t> tag(msg + m_pub_key_size + ciphertext_len,
msg + m_pub_key_size + ciphertext_len + m_mac->output_length());
valid_mask = CT::expand_mask<uint8_t>(constant_time_compare(tag.data(), calculated_tag.data(), tag.size()));
// decrypt
if(m_cipher)
{
if(valid_mask)
{
SymmetricKey dec_key(secret_keys.data(), cipher_key_len);
m_cipher->set_key(dec_key);
try
{
// the decryption can fail:
// e.g. Integrity_Failure is thrown if GCM is used and the message does not have a valid tag
if(m_iv.size())
{
m_cipher->start(m_iv.bits_of());
}
m_cipher->finish(ciphertext);
}
catch(...)
{
valid_mask = 0;
}
}
else
{
return secure_vector<uint8_t>();
}
}
else
{
xor_buf(ciphertext, secret_keys.data(), cipher_key_len);
}
return ciphertext;
}
}
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