lib/base64.c

   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 int base64_encode(const u8 *src, int srclen, char *dst)
  33 {
  34         u32 ac = 0;
  35         int bits = 0;
  36         int i;
  37         char *cp = dst;
  38
  39         for (i = 0; i < srclen; i++) {
  40                 ac = (ac << 8) | src[i];
  41                 bits += 8;
  42                 do {
  43                         bits -= 6;
  44                         *cp++ = base64_table[(ac >> bits) & 0x3f];
  45                 } while (bits >= 6);
  46         }
  47         if (bits) {
  48                 *cp++ = base64_table[(ac << (6 - bits)) & 0x3f];
  49                 bits -= 6;
  50         }
  51         while (bits < 0) {
  52                 *cp++ = '=';
  53                 bits += 2;
  54         }
  55         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 int base64_decode(const char *src, int srclen, u8 *dst)
  74 {
  75         u32 ac = 0;
  76         int bits = 0;
  77         int i;
  78         u8 *bp = dst;
  79
  80         for (i = 0; i < srclen; i++) {
  81                 const char *p = strchr(base64_table, src[i]);
  82
  83                 if (src[i] == '=') {
  84                         ac = (ac << 6);
  85                         bits += 6;
  86                         if (bits >= 8)
  87                                 bits -= 8;
  88                         continue;
  89                 }
  90                 if (p == NULL || src[i] == 0)
  91                         return -1;
  92                 ac = (ac << 6) | (p - base64_table);
  93                 bits += 6;
  94                 if (bits >= 8) {
  95                         bits -= 8;
  96                         *bp++ = (u8)(ac >> bits);
  97                 }
  98         }
  99         if (ac & ((1 << bits) - 1))
 100                 return -1;
 101         return bp - dst;
 102 }
 103 EXPORT_SYMBOL_GPL(base64_decode);