util-base64.c

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/* Copyright (C) 2007-2012 Open Information Security Foundation
 *
 * You can copy, redistribute or modify this Program under the terms of
 * the GNU General Public License version 2 as published by the Free
 * Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * version 2 along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
 * 02110-1301, USA.
 */

/**
 * \file
 *
 * \author David Abarbanel <david.abarbanel@baesystems.com>
 *
 */

#include "util-base64.h"

/* Constants */
#define BASE64_TABLE_MAX  122

/* Base64 character to index conversion table */
/* Characters are mapped as "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/" */
static const int b64table[] = { -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
        -1, -1, -1, 62, -1, -1, -1, 63, 52, 53,
        54, 55, 56, 57, 58, 59, 60, 61, -1, -1,
        -1, -1, -1, -1, -1, 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, -1, -1, -1, -1, -1, -1, 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 };

/**
 * \brief Gets a base64-decoded value from an encoded character
 *
 * \param c The encoded character
 *
 * \return The decoded value (0 or above), or -1 if the parameter is invalid
 */
static inline int GetBase64Value(uint8_t c)
{
    int val = -1;

    /* Pull from conversion table */
    if (c <= BASE64_TABLE_MAX) {
        val = b64table[(int) c];
    }

    return val;
}

/**
 * \brief Decodes a 4-byte base64-encoded block into a 3-byte ascii-encoded block
 *
 * \param ascii the 3-byte ascii output block
 * \param b64 the 4-byte base64 input block
 *
 * \return none
 */
static inline void DecodeBase64Block(uint8_t ascii[ASCII_BLOCK], uint8_t b64[B64_BLOCK])
{
    ascii[0] = (uint8_t) (b64[0] << 2) | (b64[1] >> 4);
    ascii[1] = (uint8_t) (b64[1] << 4) | (b64[2] >> 2);
    ascii[2] = (uint8_t) (b64[2] << 6) | (b64[3]);
}

/**
 * \brief Decodes a base64-encoded string buffer into an ascii-encoded byte buffer
 *
 * \param dest The destination byte buffer
 * \param src The source string
 * \param len The length of the source string
 * \param strict If set file on invalid byte, otherwise return what has been
 *    decoded.
 *
 * \return Number of bytes decoded, or 0 if no data is decoded or it fails
 */
uint32_t DecodeBase64(uint8_t *dest, const uint8_t *src, uint32_t len,
    int strict)
{
    int val;
    uint32_t padding = 0, numDecoded = 0, bbidx = 0, valid = 1, i;
    uint8_t *dptr = dest;
    uint8_t b64[B64_BLOCK] = { 0,0,0,0 };

    /* Traverse through each alpha-numeric letter in the source array */
    for(i = 0; i < len && src[i] != 0; i++) {

        /* Get decimal representation */
        val = GetBase64Value(src[i]);
        if (val < 0) {

            /* Invalid character found, so decoding fails */
            if (src[i] != '=') {
                valid = 0;
                if (strict) {
                    numDecoded = 0;
                }
                break;
            }
            padding++;
        }

        /* For each alpha-numeric letter in the source array, find the numeric
         * value */
        b64[bbidx++] = (val > 0 ? val : 0);

        /* Decode every 4 base64 bytes into 3 ascii bytes */
        if (bbidx == B64_BLOCK) {

            /* For every 4 bytes, add 3 bytes but deduct the '=' padded blocks */
            numDecoded += ASCII_BLOCK - (padding < B64_BLOCK ?
                    padding : ASCII_BLOCK);

            /* Decode base-64 block into ascii block and move pointer */
            DecodeBase64Block(dptr, b64);
            dptr += ASCII_BLOCK;

            /* Reset base-64 block and index */
            bbidx = 0;
            padding = 0;
        }
    }

    /* Finish remaining b64 bytes by padding */
    if (valid && bbidx > 0) {

        /* Decode remaining */
        numDecoded += ASCII_BLOCK - (B64_BLOCK - bbidx);
        DecodeBase64Block(dptr, b64);
    }

    if (numDecoded == 0) {
        SCLogDebug("base64 decoding failed");
    }

    return numDecoded;
}