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/*
* ChaCha20Poly1305 AEAD
* (C) 2014 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
#include <botan/internal/mode_utils.h>
#include <botan/chacha20poly1305.h>
namespace Botan {
ChaCha20Poly1305_Mode::ChaCha20Poly1305_Mode() :
m_chacha(make_stream_cipher("ChaCha")),
m_poly1305(make_message_auth("Poly1305"))
{}
bool ChaCha20Poly1305_Mode::valid_nonce_length(size_t n) const
{
return (n == 8 || n == 12);
}
void ChaCha20Poly1305_Mode::clear()
{
m_chacha->clear();
m_poly1305->clear();
m_ad.clear();
m_ctext_len = 0;
}
void ChaCha20Poly1305_Mode::key_schedule(const byte key[], size_t length)
{
m_chacha->set_key(key, length);
}
void ChaCha20Poly1305_Mode::set_associated_data(const byte ad[], size_t length)
{
if(m_ctext_len)
throw std::runtime_error("Too late to set AD for ChaCha20Poly1305");
m_ad.assign(ad, ad + length);
}
void ChaCha20Poly1305_Mode::update_len(size_t len)
{
byte len8[8] = { 0 };
store_le(static_cast<u64bit>(len), len8);
m_poly1305->update(len8, 8);
}
secure_vector<byte> ChaCha20Poly1305_Mode::start_raw(const byte nonce[], size_t nonce_len)
{
if(!valid_nonce_length(nonce_len))
throw Invalid_IV_Length(name(), nonce_len);
m_ctext_len = 0;
m_nonce_len = nonce_len;
m_chacha->set_iv(nonce, nonce_len);
secure_vector<byte> zeros(64);
m_chacha->encrypt(zeros);
m_poly1305->set_key(zeros.data(), 32);
// Remainder of output is discard
m_poly1305->update(m_ad);
if(cfrg_version())
{
std::vector<byte> padding(16 - m_ad.size() % 16);
m_poly1305->update(padding);
}
else
{
update_len(m_ad.size());
}
return secure_vector<byte>();
}
void ChaCha20Poly1305_Encryption::update(secure_vector<byte>& buffer, size_t offset)
{
BOTAN_ASSERT(buffer.size() >= offset, "Offset is sane");
const size_t sz = buffer.size() - offset;
byte* buf = buffer.data() + offset;
m_chacha->cipher1(buf, sz);
m_poly1305->update(buf, sz); // poly1305 of ciphertext
m_ctext_len += sz;
}
void ChaCha20Poly1305_Encryption::finish(secure_vector<byte>& buffer, size_t offset)
{
update(buffer, offset);
if(cfrg_version())
{
std::vector<byte> padding(16 - m_ctext_len % 16);
m_poly1305->update(padding);
update_len(m_ad.size());
}
update_len(m_ctext_len);
const secure_vector<byte> mac = m_poly1305->final();
buffer += std::make_pair(mac.data(), tag_size());
m_ctext_len = 0;
}
void ChaCha20Poly1305_Decryption::update(secure_vector<byte>& buffer, size_t offset)
{
BOTAN_ASSERT(buffer.size() >= offset, "Offset is sane");
const size_t sz = buffer.size() - offset;
byte* buf = buffer.data() + offset;
m_poly1305->update(buf, sz); // poly1305 of ciphertext
m_chacha->cipher1(buf, sz);
m_ctext_len += sz;
}
void ChaCha20Poly1305_Decryption::finish(secure_vector<byte>& buffer, size_t offset)
{
BOTAN_ASSERT(buffer.size() >= offset, "Offset is sane");
const size_t sz = buffer.size() - offset;
byte* buf = buffer.data() + offset;
BOTAN_ASSERT(sz >= tag_size(), "Have the tag as part of final input");
const size_t remaining = sz - tag_size();
if(remaining)
{
m_poly1305->update(buf, remaining); // poly1305 of ciphertext
m_chacha->cipher1(buf, remaining);
m_ctext_len += remaining;
}
if(cfrg_version())
{
for(size_t i = 0; i != 16 - m_ctext_len % 16; ++i)
m_poly1305->update(0);
update_len(m_ad.size());
}
update_len(m_ctext_len);
const secure_vector<byte> mac = m_poly1305->final();
const byte* included_tag = &buf[remaining];
m_ctext_len = 0;
if(!same_mem(mac.data(), included_tag, tag_size()))
throw Integrity_Failure("ChaCha20Poly1305 tag check failed");
buffer.resize(offset + remaining);
}
}
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