xref: /linux/lib/base64.c (revision f9bff0e31881d03badf191d3b0005839391f5f2b)
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);
104