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
18static 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 */
32int 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}
57EXPORT_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 */
73int 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}
103EXPORT_SYMBOL_GPL(base64_decode);
104