openssl/providers/common/ciphers/block.c

/*
 * Copyright 2019 The OpenSSL Project Authors. All Rights Reserved.
 *
 * Licensed under the Apache License 2.0 (the "License").  You may not use
 * this file except in compliance with the License.  You can obtain a copy
 * in the file LICENSE in the source distribution or at
 * https://www.openssl.org/source/license.html
 */

#include <string.h>
#include <openssl/evp.h>
#include <openssl/err.h>
#include "ciphers_locl.h"
#include <assert.h>

/*
 * Fills a single block of buffered data from the input, and returns the amount
 * of data remaining in the input that is a multiple of the blocksize. The buffer
 * is only filled if it already has some data in it, isn't full already or we
 * don't have at least one block in the input.
 *
 * buf: a buffer of blocksize bytes
 * buflen: contains the amount of data already in buf on entry. Updated with the
 *         amount of data in buf at the end. On entry *buflen must always be
 *         less than the blocksize
 * blocksize: size of a block. Must be greater than 0 and a power of 2
 * in: pointer to a pointer containing the input data
 * inlen: amount of input data available
 *
 * On return buf is filled with as much data as possible up to a full block,
 * *buflen is updated containing the amount of data in buf. *in is updated to
 * the new location where input data should be read from, *inlen is updated with
 * the remaining amount of data in *in. Returns the largest value <= *inlen
 * which is a multiple of the blocksize.
 */
size_t fillblock(unsigned char *buf, size_t *buflen, size_t blocksize,
                 const unsigned char **in, size_t *inlen)
{
    size_t blockmask = ~(blocksize - 1);

    assert(*buflen <= blocksize);
    assert(blocksize > 0 && (blocksize & (blocksize - 1)) == 0);

    if (*buflen != blocksize && (*buflen != 0 || *inlen < blocksize)) {
        size_t bufremain = blocksize - *buflen;

        if (*inlen < bufremain)
            bufremain = *inlen;
        memcpy(buf + *buflen, *in, bufremain);
        *in += bufremain;
        *inlen -= bufremain;
        *buflen += bufremain;
    }

    return *inlen & blockmask;
}

/*
 * Fills the buffer with trailing data from an encryption/decryption that didn't
 * fit into a full block.
 */
int trailingdata(unsigned char *buf, size_t *buflen, size_t blocksize,
                 const unsigned char **in, size_t *inlen)
{
    if (*inlen == 0)
        return 1;

    if (*buflen + *inlen > blocksize)
        return 0;

    memcpy(buf + *buflen, *in, *inlen);
    *buflen += *inlen;
    *inlen = 0;

    return 1;
}

/* Pad the final block for encryption */
void padblock(unsigned char *buf, size_t *buflen, size_t blocksize)
{
    size_t i;
    unsigned char pad = (unsigned char)(blocksize - *buflen);

    for (i = *buflen; i < blocksize; i++)
        buf[i] = pad;
}

int unpadblock(unsigned char *buf, size_t *buflen, size_t blocksize)
{
    size_t pad, i;
    size_t len = *buflen;

    if(len != blocksize)
        return 0;

    /*
     * The following assumes that the ciphertext has been authenticated.
     * Otherwise it provides a padding oracle.
     */
    pad = buf[blocksize - 1];
    if (pad == 0 || pad > blocksize) {
        EVPerr(EVP_F_EVP_DECRYPTFINAL_EX, EVP_R_BAD_DECRYPT);
        return 0;
    }
    for (i = 0; i < pad; i++) {
        if (buf[--len] != pad) {
            EVPerr(EVP_F_EVP_DECRYPTFINAL_EX, EVP_R_BAD_DECRYPT);
            return 0;
        }
    }
    *buflen = len;
    return 1;
}