404 lines
7.6 KiB
C
404 lines
7.6 KiB
C
/*
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* Copyright (C) 2010 Martin Willi
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* Copyright (C) 2010 revosec AG
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*
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* This program is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License as published by the
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* Free Software Foundation; either version 2 of the License, or (at your
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* option) any later version. See <http://www.fsf.org/copyleft/gpl.txt>.
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*
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* This program is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
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* or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* for more details.
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*/
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#include "gcm_aead.h"
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#include <debug.h>
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#define BLOCK_SIZE 16
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#define NONCE_SIZE 12
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#define IV_SIZE 8
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#define SALT_SIZE (NONCE_SIZE - IV_SIZE)
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typedef struct private_gcm_aead_t private_gcm_aead_t;
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/**
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* Private data of an gcm_aead_t object.
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*/
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struct private_gcm_aead_t {
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/**
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* Public gcm_aead_t interface.
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*/
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gcm_aead_t public;
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/**
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* Underlying CBC crypter.
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*/
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crypter_t *crypter;
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/**
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* Size of the integrity check value
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*/
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size_t icv_size;
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/**
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* Salt value
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*/
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char salt[SALT_SIZE];
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/**
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* GHASH subkey H
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*/
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char h[BLOCK_SIZE];
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};
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/**
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* Bitshift a block right by one bit
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*/
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static void sr_block(u_char *block)
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{
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int i;
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for (i = BLOCK_SIZE - 1; i >= 0; i--)
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{
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block[i] = block[i] >> 1;
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if (i != 0)
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{
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block[i] |= block[i - 1] << 7;
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}
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}
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}
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/**
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* Naive implementation of block multiplication in GF128, no tables
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*/
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static void mult_block(char *x, char *y, char *res)
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{
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char z[BLOCK_SIZE], v[BLOCK_SIZE], r;
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int bit, byte;
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r = 0xE1;
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memset(z, 0, BLOCK_SIZE);
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memcpy(v, y, BLOCK_SIZE);
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for (byte = 0; byte < BLOCK_SIZE; byte++)
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{
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for (bit = 7; bit >= 0; bit--)
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{
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if (x[byte] & (1 << bit))
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{
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memxor(z, v, BLOCK_SIZE);
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}
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if (v[BLOCK_SIZE - 1] & 0x01)
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{
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sr_block(v);
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v[0] ^= r;
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}
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else
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{
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sr_block(v);
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}
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}
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}
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memcpy(res, z, BLOCK_SIZE);
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}
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/**
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* GHASH function
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*/
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static void ghash(private_gcm_aead_t *this, chunk_t x, char *res)
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{
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char y[BLOCK_SIZE];
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memset(y, 0, BLOCK_SIZE);
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while (x.len)
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{
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memxor(y, x.ptr, BLOCK_SIZE);
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mult_block(y, this->h, y);
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x = chunk_skip(x, BLOCK_SIZE);
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}
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memcpy(res, y, BLOCK_SIZE);
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}
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/**
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* GCTR function, en-/decrypts x inline
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*/
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static void gctr(private_gcm_aead_t *this, char *icb, chunk_t x)
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{
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char cb[BLOCK_SIZE], iv[BLOCK_SIZE], tmp[BLOCK_SIZE];
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memset(iv, 0, BLOCK_SIZE);
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memcpy(cb, icb, BLOCK_SIZE);
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while (x.len)
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{
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memcpy(tmp, cb, BLOCK_SIZE);
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this->crypter->encrypt(this->crypter, chunk_from_thing(tmp),
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chunk_from_thing(iv), NULL);
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memxor(x.ptr, tmp, min(BLOCK_SIZE, x.len));
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chunk_increment(chunk_from_thing(cb));
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x = chunk_skip(x, BLOCK_SIZE);
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}
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}
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/**
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* Generate the block J0
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*/
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static void create_j(private_gcm_aead_t *this, char *iv, char *j)
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{
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memcpy(j, this->salt, SALT_SIZE);
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memcpy(j + SALT_SIZE, iv, IV_SIZE);
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htoun32(j + SALT_SIZE + IV_SIZE, 1);
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}
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/**
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* Create GHASH subkey H
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*/
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static void create_h(private_gcm_aead_t *this, char *h)
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{
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char zero[BLOCK_SIZE];
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memset(zero, 0, BLOCK_SIZE);
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memset(h, 0, BLOCK_SIZE);
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this->crypter->encrypt(this->crypter, chunk_create(h, BLOCK_SIZE),
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chunk_from_thing(zero), NULL);
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}
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/**
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* Encrypt/decrypt
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*/
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static void crypt(private_gcm_aead_t *this, char *j, chunk_t in, chunk_t out)
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{
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char icb[BLOCK_SIZE];
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memcpy(icb, j, BLOCK_SIZE);
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chunk_increment(chunk_from_thing(icb));
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out.len = in.len;
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if (in.ptr != out.ptr)
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{
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memcpy(out.ptr, in.ptr, in.len);
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}
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gctr(this, icb, out);
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}
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/**
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* Create ICV
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*/
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static void create_icv(private_gcm_aead_t *this, chunk_t assoc, chunk_t crypt,
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char *j, char *icv)
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{
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size_t assoc_pad, crypt_pad;
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chunk_t chunk;
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char s[BLOCK_SIZE], *pos;
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assoc_pad = (BLOCK_SIZE - (assoc.len % BLOCK_SIZE)) % BLOCK_SIZE;
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crypt_pad = (BLOCK_SIZE - (crypt.len % BLOCK_SIZE)) % BLOCK_SIZE;
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/* concatenate data to a new chunk */
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chunk = chunk_alloc(assoc.len + assoc_pad +
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crypt.len + crypt_pad + BLOCK_SIZE);
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pos = chunk.ptr;
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/* add associated data */
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memcpy(pos, assoc.ptr, assoc.len);
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pos += assoc.len;
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memset(pos, 0, assoc_pad);
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pos += assoc_pad;
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/* add encrypted data */
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memcpy(pos, crypt.ptr, crypt.len);
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pos += crypt.len;
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memset(pos, 0, crypt_pad);
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pos += crypt_pad;
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/* write associated len */
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memset(pos, 0, 4);
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pos += 4;
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htoun32(pos, assoc.len * 8);
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pos += 4;
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/* write encrypted length */
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memset(pos, 0, 4);
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pos += 4;
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htoun32(pos, crypt.len * 8);
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pos += 4;
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ghash(this, chunk, s);
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free(chunk.ptr);
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gctr(this, j, chunk_from_thing(s));
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memcpy(icv, s, this->icv_size);
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}
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/**
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* Verify the ICV value
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*/
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static bool verify_icv(private_gcm_aead_t *this, chunk_t assoc, chunk_t crypt,
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char *j, char *icv)
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{
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char tmp[this->icv_size];
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create_icv(this, assoc, crypt, j, tmp);
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return memeq(tmp, icv, this->icv_size);
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}
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METHOD(aead_t, encrypt, void,
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private_gcm_aead_t *this, chunk_t plain, chunk_t assoc, chunk_t iv,
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chunk_t *encrypted)
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{
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char j[BLOCK_SIZE];
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create_j(this, iv.ptr, j);
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if (encrypted)
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{
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*encrypted = chunk_alloc(plain.len + this->icv_size);
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crypt(this, j, plain, *encrypted);
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create_icv(this, assoc,
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chunk_create(encrypted->ptr, encrypted->len - this->icv_size),
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j, encrypted->ptr + encrypted->len - this->icv_size);
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}
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else
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{
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crypt(this, j, plain, plain);
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create_icv(this, assoc, plain, j, plain.ptr + plain.len);
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}
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}
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METHOD(aead_t, decrypt, bool,
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private_gcm_aead_t *this, chunk_t encrypted, chunk_t assoc, chunk_t iv,
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chunk_t *plain)
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{
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char j[BLOCK_SIZE];
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if (encrypted.len < this->icv_size)
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{
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return FALSE;
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}
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create_j(this, iv.ptr, j);
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encrypted.len -= this->icv_size;
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if (!verify_icv(this, assoc, encrypted, j, encrypted.ptr + encrypted.len))
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{
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return FALSE;
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}
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if (plain)
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{
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*plain = chunk_alloc(encrypted.len);
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crypt(this, j, encrypted, *plain);
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}
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else
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{
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crypt(this, j, encrypted, encrypted);
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}
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return TRUE;
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}
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METHOD(aead_t, get_block_size, size_t,
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private_gcm_aead_t *this)
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{
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return 1;
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}
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METHOD(aead_t, get_icv_size, size_t,
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private_gcm_aead_t *this)
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{
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return this->icv_size;
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}
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METHOD(aead_t, get_iv_size, size_t,
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private_gcm_aead_t *this)
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{
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return IV_SIZE;
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}
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METHOD(aead_t, get_key_size, size_t,
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private_gcm_aead_t *this)
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{
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return this->crypter->get_key_size(this->crypter) + SALT_SIZE;
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}
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METHOD(aead_t, set_key, void,
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private_gcm_aead_t *this, chunk_t key)
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{
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memcpy(this->salt, key.ptr + key.len - SALT_SIZE, SALT_SIZE);
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key.len -= SALT_SIZE;
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this->crypter->set_key(this->crypter, key);
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create_h(this, this->h);
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}
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METHOD(aead_t, destroy, void,
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private_gcm_aead_t *this)
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{
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this->crypter->destroy(this->crypter);
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free(this);
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}
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/**
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* See header
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*/
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gcm_aead_t *gcm_aead_create(encryption_algorithm_t algo, size_t key_size)
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{
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private_gcm_aead_t *this;
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size_t icv_size;
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switch (key_size)
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{
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case 0:
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key_size = 16;
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break;
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case 16:
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case 24:
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case 32:
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break;
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default:
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return NULL;
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}
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switch (algo)
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{
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case ENCR_AES_GCM_ICV8:
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algo = ENCR_AES_CBC;
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icv_size = 8;
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break;
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case ENCR_AES_GCM_ICV12:
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algo = ENCR_AES_CBC;
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icv_size = 12;
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break;
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case ENCR_AES_GCM_ICV16:
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algo = ENCR_AES_CBC;
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icv_size = 16;
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break;
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default:
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return NULL;
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}
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INIT(this,
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.public = {
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.aead = {
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.encrypt = _encrypt,
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.decrypt = _decrypt,
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.get_block_size = _get_block_size,
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.get_icv_size = _get_icv_size,
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.get_iv_size = _get_iv_size,
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.get_key_size = _get_key_size,
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.set_key = _set_key,
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.destroy = _destroy,
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},
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},
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.crypter = lib->crypto->create_crypter(lib->crypto, algo, key_size),
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.icv_size = icv_size,
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);
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if (!this->crypter)
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{
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free(this);
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return NULL;
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}
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return &this->public;
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}
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