the-tree/lib/base64.c

0001 // SPDX-License-Identifier: GPL-2.0
0002 /*
0003  * base64.c - RFC4648-compliant base64 encoding
0004  *
0005  * Copyright (c) 2020 Hannes Reinecke, SUSE
0006  *
0007  * Based on the base64url routines from fs/crypto/fname.c
0008  * (which are using the URL-safe base64 encoding),
0009  * modified to use the standard coding table from RFC4648 section 4.
0010  */
0011
0012 #include <linux/kernel.h>
0013 #include <linux/types.h>
0014 #include <linux/export.h>
0015 #include <linux/string.h>
0016 #include <linux/base64.h>
0017
0018 static const char base64_table[65] =
0019     "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
0020
0021 /**
0022  * base64_encode() - base64-encode some binary data
0023  * @src: the binary data to encode
0024  * @srclen: the length of @src in bytes
0025  * @dst: (output) the base64-encoded string.  Not NUL-terminated.
0026  *
0027  * Encodes data using base64 encoding, i.e. the "Base 64 Encoding" specified
0028  * by RFC 4648, including the  '='-padding.
0029  *
0030  * Return: the length of the resulting base64-encoded string in bytes.
0031  */
0032 int base64_encode(const u8 *src, int srclen, char *dst)
0033 {
0034     u32 ac = 0;
0035     int bits = 0;
0036     int i;
0037     char *cp = dst;
0038
0039     for (i = 0; i < srclen; i++) {
0040         ac = (ac << 8) | src[i];
0041         bits += 8;
0042         do {
0043             bits -= 6;
0044             *cp++ = base64_table[(ac >> bits) & 0x3f];
0045         } while (bits >= 6);
0046     }
0047     if (bits) {
0048         *cp++ = base64_table[(ac << (6 - bits)) & 0x3f];
0049         bits -= 6;
0050     }
0051     while (bits < 0) {
0052         *cp++ = '=';
0053         bits += 2;
0054     }
0055     return cp - dst;
0056 }
0057 EXPORT_SYMBOL_GPL(base64_encode);
0058
0059 /**
0060  * base64_decode() - base64-decode a string
0061  * @src: the string to decode.  Doesn't need to be NUL-terminated.
0062  * @srclen: the length of @src in bytes
0063  * @dst: (output) the decoded binary data
0064  *
0065  * Decodes a string using base64 encoding, i.e. the "Base 64 Encoding"
0066  * specified by RFC 4648, including the  '='-padding.
0067  *
0068  * This implementation hasn't been optimized for performance.
0069  *
0070  * Return: the length of the resulting decoded binary data in bytes,
0071  *     or -1 if the string isn't a valid base64 string.
0072  */
0073 int base64_decode(const char *src, int srclen, u8 *dst)
0074 {
0075     u32 ac = 0;
0076     int bits = 0;
0077     int i;
0078     u8 *bp = dst;
0079
0080     for (i = 0; i < srclen; i++) {
0081         const char *p = strchr(base64_table, src[i]);
0082
0083         if (src[i] == '=') {
0084             ac = (ac << 6);
0085             bits += 6;
0086             if (bits >= 8)
0087                 bits -= 8;
0088             continue;
0089         }
0090         if (p == NULL || src[i] == 0)
0091             return -1;
0092         ac = (ac << 6) | (p - base64_table);
0093         bits += 6;
0094         if (bits >= 8) {
0095             bits -= 8;
0096             *bp++ = (u8)(ac >> bits);
0097         }
0098     }
0099     if (ac & ((1 << bits) - 1))
0100         return -1;
0101     return bp - dst;
0102 }
0103 EXPORT_SYMBOL_GPL(base64_decode);