library/base64.c

/*
 *  RFC 1521 base64 encoding/decoding
 *
 *  Copyright The Mbed TLS Contributors
 *  SPDX-License-Identifier: Apache-2.0
 *
 *  Licensed under the Apache License, Version 2.0 (the "License"); you may
 *  not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *  http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */

#include "common.h"

#if defined(MBEDTLS_BASE64_C)

#    include "mbedtls/base64.h"

#    include <stdint.h>

#    if defined(MBEDTLS_SELF_TEST)
#        include <string.h>
#        if defined(MBEDTLS_PLATFORM_C)
#            include "mbedtls/platform.h"
#        else
#            include <stdio.h>
#            define mbedtls_printf printf
#        endif /* MBEDTLS_PLATFORM_C */
#    endif /* MBEDTLS_SELF_TEST */

static const unsigned char base64_enc_map[64] = {
    'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M',
    'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z',
    'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm',
    'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z',
    '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '+', '/'
};

static const unsigned char base64_dec_map[128] = {
    127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127,
    127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127,
    127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 62,  127,
    127, 127, 63,  52,  53,  54,  55,  56,  57,  58,  59,  60,  61,  127, 127,
    127, 64,  127, 127, 127, 0,   1,   2,   3,   4,   5,   6,   7,   8,   9,
    10,  11,  12,  13,  14,  15,  16,  17,  18,  19,  20,  21,  22,  23,  24,
    25,  127, 127, 127, 127, 127, 127, 26,  27,  28,  29,  30,  31,  32,  33,
    34,  35,  36,  37,  38,  39,  40,  41,  42,  43,  44,  45,  46,  47,  48,
    49,  50,  51,  127, 127, 127, 127, 127
};

#    define BASE64_SIZE_T_MAX ((size_t)-1) /* SIZE_T_MAX is not standard */

/*
 * Constant flow conditional assignment to unsigned char
 */
static void mbedtls_base64_cond_assign_uchar(unsigned char *dest,
                                             const unsigned char *const src,
                                             unsigned char condition)
{
    /* MSVC has a warning about unary minus on unsigned integer types,
     * but this is well-defined and precisely what we want to do here. */
#    if defined(_MSC_VER)
#        pragma warning(push)
#        pragma warning(disable : 4146)
#    endif

    /* Generate bitmask from condition, mask will either be 0xFF or 0 */
    unsigned char mask = (condition | -condition);
    mask >>= 7;
    mask = -mask;

#    if defined(_MSC_VER)
#        pragma warning(pop)
#    endif

    *dest = ((*src) & mask) | ((*dest) & ~mask);
}

/*
 * Constant flow conditional assignment to uint_32
 */
static void mbedtls_base64_cond_assign_uint32(uint32_t *dest,
                                              const uint32_t src,
                                              uint32_t condition)
{
    /* MSVC has a warning about unary minus on unsigned integer types,
     * but this is well-defined and precisely what we want to do here. */
#    if defined(_MSC_VER)
#        pragma warning(push)
#        pragma warning(disable : 4146)
#    endif

    /* Generate bitmask from condition, mask will either be 0xFFFFFFFF or 0 */
    uint32_t mask = (condition | -condition);
    mask >>= 31;
    mask = -mask;

#    if defined(_MSC_VER)
#        pragma warning(pop)
#    endif

    *dest = (src & mask) | ((*dest) & ~mask);
}

/*
 * Constant flow check for equality
 */
static unsigned char mbedtls_base64_eq(size_t in_a, size_t in_b)
{
    size_t difference = in_a ^ in_b;

    /* MSVC has a warning about unary minus on unsigned integer types,
     * but this is well-defined and precisely what we want to do here. */
#    if defined(_MSC_VER)
#        pragma warning(push)
#        pragma warning(disable : 4146)
#    endif

    difference |= -difference;

#    if defined(_MSC_VER)
#        pragma warning(pop)
#    endif

    /* cope with the varying size of size_t per platform */
    difference >>= (sizeof(difference) * 8 - 1);

    return (unsigned char)(1 ^ difference);
}

/*
 * Constant flow lookup into table.
 */
static unsigned char
mbedtls_base64_table_lookup(const unsigned char *const table,
                            const size_t table_size,
                            const size_t table_index)
{
    size_t i;
    unsigned char result = 0;

    for (i = 0; i < table_size; ++i) {
        mbedtls_base64_cond_assign_uchar(&result, &table[i],
                                         mbedtls_base64_eq(i, table_index));
    }

    return result;
}

/*
 * Encode a buffer into base64 format
 */
int mbedtls_base64_encode(unsigned char *dst,
                          size_t dlen,
                          size_t *olen,
                          const unsigned char *src,
                          size_t slen)
{
    size_t i, n;
    int C1, C2, C3;
    unsigned char *p;

    if (slen == 0) {
        *olen = 0;
        return 0;
    }

    n = slen / 3 + (slen % 3 != 0);

    if (n > (BASE64_SIZE_T_MAX - 1) / 4) {
        *olen = BASE64_SIZE_T_MAX;
        return MBEDTLS_ERR_BASE64_BUFFER_TOO_SMALL;
    }

    n *= 4;

    if ((dlen < n + 1) || (NULL == dst)) {
        *olen = n + 1;
        return MBEDTLS_ERR_BASE64_BUFFER_TOO_SMALL;
    }

    n = (slen / 3) * 3;

    for (i = 0, p = dst; i < n; i += 3) {
        C1 = *src++;
        C2 = *src++;
        C3 = *src++;

        *p++ = mbedtls_base64_table_lookup(
            base64_enc_map, sizeof(base64_enc_map), ((C1 >> 2) & 0x3F));

        *p++ =
            mbedtls_base64_table_lookup(base64_enc_map, sizeof(base64_enc_map),
                                        ((((C1 & 3) << 4) + (C2 >> 4)) & 0x3F));

        *p++ = mbedtls_base64_table_lookup(
            base64_enc_map, sizeof(base64_enc_map),
            ((((C2 & 15) << 2) + (C3 >> 6)) & 0x3F));

        *p++ = mbedtls_base64_table_lookup(base64_enc_map,
                                           sizeof(base64_enc_map), (C3 & 0x3F));
    }

    if (i < slen) {
        C1 = *src++;
        C2 = ((i + 1) < slen) ? *src++ : 0;

        *p++ = mbedtls_base64_table_lookup(
            base64_enc_map, sizeof(base64_enc_map), ((C1 >> 2) & 0x3F));

        *p++ =
            mbedtls_base64_table_lookup(base64_enc_map, sizeof(base64_enc_map),
                                        ((((C1 & 3) << 4) + (C2 >> 4)) & 0x3F));

        if ((i + 1) < slen)
            *p++ = mbedtls_base64_table_lookup(base64_enc_map,
                                               sizeof(base64_enc_map),
                                               (((C2 & 15) << 2) & 0x3F));
        else
            *p++ = '=';

        *p++ = '=';
    }

    *olen = p - dst;
    *p = 0;

    return 0;
}

/*
 * Decode a base64-formatted buffer
 */
int mbedtls_base64_decode(unsigned char *dst,
                          size_t dlen,
                          size_t *olen,
                          const unsigned char *src,
                          size_t slen)
{
    size_t i, n;
    uint32_t j, x;
    unsigned char *p;
    unsigned char dec_map_lookup;

    /* First pass: check for validity and get output length */
    for (i = n = j = 0; i < slen; i++) {
        /* Skip spaces before checking for EOL */
        x = 0;
        while (i < slen && src[i] == ' ') {
            ++i;
            ++x;
        }

        /* Spaces at end of buffer are OK */
        if (i == slen)
            break;

        if ((slen - i) >= 2 && src[i] == '\r' && src[i + 1] == '\n')
            continue;

        if (src[i] == '\n')
            continue;

        /* Space inside a line is an error */
        if (x != 0)
            return MBEDTLS_ERR_BASE64_INVALID_CHARACTER;

        if (src[i] == '=' && ++j > 2)
            return MBEDTLS_ERR_BASE64_INVALID_CHARACTER;

        dec_map_lookup = mbedtls_base64_table_lookup(
            base64_dec_map, sizeof(base64_dec_map), src[i]);

        if (src[i] > 127 || dec_map_lookup == 127)
            return MBEDTLS_ERR_BASE64_INVALID_CHARACTER;

        if (dec_map_lookup < 64 && j != 0)
            return MBEDTLS_ERR_BASE64_INVALID_CHARACTER;

        n++;
    }

    if (n == 0) {
        *olen = 0;
        return 0;
    }

    /* The following expression is to calculate the following formula without
     * risk of integer overflow in n:
     *     n = ( ( n * 6 ) + 7 ) >> 3;
     */
    n = (6 * (n >> 3)) + ((6 * (n & 0x7) + 7) >> 3);
    n -= j;

    if (dst == NULL || dlen < n) {
        *olen = n;
        return MBEDTLS_ERR_BASE64_BUFFER_TOO_SMALL;
    }

    for (j = 3, n = x = 0, p = dst; i > 0; i--, src++) {
        if (*src == '\r' || *src == '\n' || *src == ' ')
            continue;

        dec_map_lookup = mbedtls_base64_table_lookup(
            base64_dec_map, sizeof(base64_dec_map), *src);

        mbedtls_base64_cond_assign_uint32(
            &j, j - 1, mbedtls_base64_eq(dec_map_lookup, 64));
        x = (x << 6) | (dec_map_lookup & 0x3F);

        if (++n == 4) {
            n = 0;
            if (j > 0)
                *p++ = (unsigned char)(x >> 16);
            if (j > 1)
                *p++ = (unsigned char)(x >> 8);
            if (j > 2)
                *p++ = (unsigned char)(x);
        }
    }

    *olen = p - dst;

    return 0;
}

#    if defined(MBEDTLS_SELF_TEST)

static const unsigned char base64_test_dec[64] = {
    0x24, 0x48, 0x6E, 0x56, 0x87, 0x62, 0x5A, 0xBD, 0xBF, 0x17, 0xD9,
    0xA2, 0xC4, 0x17, 0x1A, 0x01, 0x94, 0xED, 0x8F, 0x1E, 0x11, 0xB3,
    0xD7, 0x09, 0x0C, 0xB6, 0xE9, 0x10, 0x6F, 0x22, 0xEE, 0x13, 0xCA,
    0xB3, 0x07, 0x05, 0x76, 0xC9, 0xFA, 0x31, 0x6C, 0x08, 0x34, 0xFF,
    0x8D, 0xC2, 0x6C, 0x38, 0x00, 0x43, 0xE9, 0x54, 0x97, 0xAF, 0x50,
    0x4B, 0xD1, 0x41, 0xBA, 0x95, 0x31, 0x5A, 0x0B, 0x97
};

static const unsigned char base64_test_enc[] =
    "JEhuVodiWr2/F9mixBcaAZTtjx4Rs9cJDLbpEG8i7hPK"
    "swcFdsn6MWwINP+Nwmw4AEPpVJevUEvRQbqVMVoLlw==";

/*
 * Checkup routine
 */
int mbedtls_base64_self_test(int verbose)
{
    size_t len;
    const unsigned char *src;
    unsigned char buffer[128];

    if (verbose != 0)
        mbedtls_printf("  Base64 encoding test: ");

    src = base64_test_dec;

    if (mbedtls_base64_encode(buffer, sizeof(buffer), &len, src, 64) != 0 ||
        memcmp(base64_test_enc, buffer, 88) != 0) {
        if (verbose != 0)
            mbedtls_printf("failed\n");

        return 1;
    }

    if (verbose != 0)
        mbedtls_printf("passed\n  Base64 decoding test: ");

    src = base64_test_enc;

    if (mbedtls_base64_decode(buffer, sizeof(buffer), &len, src, 88) != 0 ||
        memcmp(base64_test_dec, buffer, 64) != 0) {
        if (verbose != 0)
            mbedtls_printf("failed\n");

        return 1;
    }

    if (verbose != 0)
        mbedtls_printf("passed\n\n");

    return 0;
}

#    endif /* MBEDTLS_SELF_TEST */

#endif /* MBEDTLS_BASE64_C */