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);