Line data    Source code

       1             : // SPDX-License-Identifier: GPL-2.0
       2             : /*
       3             :  * base64.c - RFC4648-compliant base64 encoding
       4             :  *
       5             :  * Copyright (c) 2020 Hannes Reinecke, SUSE
       6             :  *
       7             :  * Based on the base64url routines from fs/crypto/fname.c
       8             :  * (which are using the URL-safe base64 encoding),
       9             :  * modified to use the standard coding table from RFC4648 section 4.
      10             :  */
      11             : 
      12             : #include <linux/kernel.h>
      13             : #include <linux/types.h>
      14             : #include <linux/export.h>
      15             : #include <linux/string.h>
      16             : #include <linux/base64.h>
      17             : 
      18             : static const char base64_table[65] =
      19             :         "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
      20             : 
      21             : /**
      22             :  * base64_encode() - base64-encode some binary data
      23             :  * @src: the binary data to encode
      24             :  * @srclen: the length of @src in bytes
      25             :  * @dst: (output) the base64-encoded string.  Not NUL-terminated.
      26             :  *
      27             :  * Encodes data using base64 encoding, i.e. the "Base 64 Encoding" specified
      28             :  * by RFC 4648, including the  '='-padding.
      29             :  *
      30             :  * Return: the length of the resulting base64-encoded string in bytes.
      31             :  */
      32           0 : int base64_encode(const u8 *src, int srclen, char *dst)
      33             : {
      34           0 :         u32 ac = 0;
      35           0 :         int bits = 0;
      36             :         int i;
      37           0 :         char *cp = dst;
      38             : 
      39           0 :         for (i = 0; i < srclen; i++) {
      40           0 :                 ac = (ac << 8) | src[i];
      41           0 :                 bits += 8;
      42             :                 do {
      43           0 :                         bits -= 6;
      44           0 :                         *cp++ = base64_table[(ac >> bits) & 0x3f];
      45           0 :                 } while (bits >= 6);
      46             :         }
      47           0 :         if (bits) {
      48           0 :                 *cp++ = base64_table[(ac << (6 - bits)) & 0x3f];
      49           0 :                 bits -= 6;
      50             :         }
      51           0 :         while (bits < 0) {
      52           0 :                 *cp++ = '=';
      53           0 :                 bits += 2;
      54             :         }
      55           0 :         return cp - dst;
      56             : }
      57             : EXPORT_SYMBOL_GPL(base64_encode);
      58             : 
      59             : /**
      60             :  * base64_decode() - base64-decode a string
      61             :  * @src: the string to decode.  Doesn't need to be NUL-terminated.
      62             :  * @srclen: the length of @src in bytes
      63             :  * @dst: (output) the decoded binary data
      64             :  *
      65             :  * Decodes a string using base64 encoding, i.e. the "Base 64 Encoding"
      66             :  * specified by RFC 4648, including the  '='-padding.
      67             :  *
      68             :  * This implementation hasn't been optimized for performance.
      69             :  *
      70             :  * Return: the length of the resulting decoded binary data in bytes,
      71             :  *         or -1 if the string isn't a valid base64 string.
      72             :  */
      73           0 : int base64_decode(const char *src, int srclen, u8 *dst)
      74             : {
      75           0 :         u32 ac = 0;
      76           0 :         int bits = 0;
      77             :         int i;
      78           0 :         u8 *bp = dst;
      79             : 
      80           0 :         for (i = 0; i < srclen; i++) {
      81           0 :                 const char *p = strchr(base64_table, src[i]);
      82             : 
      83           0 :                 if (src[i] == '=') {
      84           0 :                         ac = (ac << 6);
      85           0 :                         bits += 6;
      86           0 :                         if (bits >= 8)
      87           0 :                                 bits -= 8;
      88           0 :                         continue;
      89             :                 }
      90           0 :                 if (p == NULL || src[i] == 0)
      91             :                         return -1;
      92           0 :                 ac = (ac << 6) | (p - base64_table);
      93           0 :                 bits += 6;
      94           0 :                 if (bits >= 8) {
      95           0 :                         bits -= 8;
      96           0 :                         *bp++ = (u8)(ac >> bits);
      97             :                 }
      98             :         }
      99           0 :         if (ac & ((1 << bits) - 1))
     100             :                 return -1;
     101           0 :         return bp - dst;
     102             : }
     103             : EXPORT_SYMBOL_GPL(base64_decode);