projects/linux·blob 2c455ddc · refs

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1// SPDX-License-Identifier: GPL-2.0
2/*
3 * base64.c - Base64 with support for multiple variants
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 support multiple Base64 variants.
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
18static const char base64_tables[][65] = {
19 [BASE64_STD] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/",
20 [BASE64_URLSAFE] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_",
21 [BASE64_IMAP] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+,",
22};
23
24/*
25 * Initialize the base64 reverse mapping for a single character
26 * This macro maps a character to its corresponding base64 value,
27 * returning -1 if the character is invalid.
28 * char 'A'-'Z' maps to 0-25, 'a'-'z' maps to 26-51, '0'-'9' maps to 52-61,
29 * ch_62 maps to 62, ch_63 maps to 63, and other characters return -1
30 */
31#define INIT_1(v, ch_62, ch_63) \
32 [v] = (v) >= 'A' && (v) <= 'Z' ? (v) - 'A' \
33 : (v) >= 'a' && (v) <= 'z' ? (v) - 'a' + 26 \
34 : (v) >= '0' && (v) <= '9' ? (v) - '0' + 52 \
35 : (v) == (ch_62) ? 62 : (v) == (ch_63) ? 63 : -1
36
37/*
38 * Recursive macros to generate multiple Base64 reverse mapping table entries.
39 * Each macro generates a sequence of entries in the lookup table:
40 * INIT_2 generates 2 entries, INIT_4 generates 4, INIT_8 generates 8, and so on up to INIT_32.
41 */
42#define INIT_2(v, ...) INIT_1(v, __VA_ARGS__), INIT_1((v) + 1, __VA_ARGS__)
43#define INIT_4(v, ...) INIT_2(v, __VA_ARGS__), INIT_2((v) + 2, __VA_ARGS__)
44#define INIT_8(v, ...) INIT_4(v, __VA_ARGS__), INIT_4((v) + 4, __VA_ARGS__)
45#define INIT_16(v, ...) INIT_8(v, __VA_ARGS__), INIT_8((v) + 8, __VA_ARGS__)
46#define INIT_32(v, ...) INIT_16(v, __VA_ARGS__), INIT_16((v) + 16, __VA_ARGS__)
47
48#define BASE64_REV_INIT(ch_62, ch_63) { \
49 [0 ... 0x1f] = -1, \
50 INIT_32(0x20, ch_62, ch_63), \
51 INIT_32(0x40, ch_62, ch_63), \
52 INIT_32(0x60, ch_62, ch_63), \
53 [0x80 ... 0xff] = -1 }
54
55static const s8 base64_rev_maps[][256] = {
56 [BASE64_STD] = BASE64_REV_INIT('+', '/'),
57 [BASE64_URLSAFE] = BASE64_REV_INIT('-', '_'),
58 [BASE64_IMAP] = BASE64_REV_INIT('+', ',')
59};
60
61#undef BASE64_REV_INIT
62#undef INIT_32
63#undef INIT_16
64#undef INIT_8
65#undef INIT_4
66#undef INIT_2
67#undef INIT_1
68/**
69 * base64_encode() - Base64-encode some binary data
70 * @src: the binary data to encode
71 * @srclen: the length of @src in bytes
72 * @dst: (output) the Base64-encoded string. Not NUL-terminated.
73 * @padding: whether to append '=' padding characters
74 * @variant: which base64 variant to use
75 *
76 * Encodes data using the selected Base64 variant.
77 *
78 * Return: the length of the resulting Base64-encoded string in bytes.
79 */
80int base64_encode(const u8 *src, int srclen, char *dst, bool padding, enum base64_variant variant)
81{
82 u32 ac = 0;
83 char *cp = dst;
84 const char *base64_table = base64_tables[variant];
85
86 while (srclen >= 3) {
87 ac = src[0] << 16 | src[1] << 8 | src[2];
88 *cp++ = base64_table[ac >> 18];
89 *cp++ = base64_table[(ac >> 12) & 0x3f];
90 *cp++ = base64_table[(ac >> 6) & 0x3f];
91 *cp++ = base64_table[ac & 0x3f];
92
93 src += 3;
94 srclen -= 3;
95 }
96
97 switch (srclen) {
98 case 2:
99 ac = src[0] << 16 | src[1] << 8;
100 *cp++ = base64_table[ac >> 18];
101 *cp++ = base64_table[(ac >> 12) & 0x3f];
102 *cp++ = base64_table[(ac >> 6) & 0x3f];
103 if (padding)
104 *cp++ = '=';
105 break;
106 case 1:
107 ac = src[0] << 16;
108 *cp++ = base64_table[ac >> 18];
109 *cp++ = base64_table[(ac >> 12) & 0x3f];
110 if (padding) {
111 *cp++ = '=';
112 *cp++ = '=';
113 }
114 break;
115 }
116 return cp - dst;
117}
118EXPORT_SYMBOL_GPL(base64_encode);
119
120/**
121 * base64_decode() - Base64-decode a string
122 * @src: the string to decode. Doesn't need to be NUL-terminated.
123 * @srclen: the length of @src in bytes
124 * @dst: (output) the decoded binary data
125 * @padding: whether the input is expected to include '=' padding characters
126 * @variant: which base64 variant to use
127 *
128 * Decodes a string using the selected Base64 variant.
129 *
130 * Return: the length of the resulting decoded binary data in bytes,
131 * or -1 if the string isn't a valid Base64 string.
132 */
133int base64_decode(const char *src, int srclen, u8 *dst, bool padding, enum base64_variant variant)
134{
135 u8 *bp = dst;
136 s8 input[4];
137 s32 val;
138 const u8 *s = (const u8 *)src;
139 const s8 *base64_rev_tables = base64_rev_maps[variant];
140
141 while (srclen >= 4) {
142 input[0] = base64_rev_tables[s[0]];
143 input[1] = base64_rev_tables[s[1]];
144 input[2] = base64_rev_tables[s[2]];
145 input[3] = base64_rev_tables[s[3]];
146
147 val = input[0] << 18 | input[1] << 12 | input[2] << 6 | input[3];
148
149 if (unlikely(val < 0)) {
150 if (!padding || srclen != 4 || s[3] != '=')
151 return -1;
152 padding = 0;
153 srclen = s[2] == '=' ? 2 : 3;
154 break;
155 }
156
157 *bp++ = val >> 16;
158 *bp++ = val >> 8;
159 *bp++ = val;
160
161 s += 4;
162 srclen -= 4;
163 }
164
165 if (likely(!srclen))
166 return bp - dst;
167 if (padding || srclen == 1)
168 return -1;
169
170 val = (base64_rev_tables[s[0]] << 12) | (base64_rev_tables[s[1]] << 6);
171
172 if (srclen == 2) {
173 if (val & 0x800003ff)
174 return -1;
175 *bp++ = val >> 10;
176 } else {
177 val |= base64_rev_tables[s[2]];
178 if (val & 0x80000003)
179 return -1;
180 *bp++ = val >> 10;
181 *bp++ = val >> 2;
182 }
183 return bp - dst;
184}
185EXPORT_SYMBOL_GPL(base64_decode);