[PATCH v5 1/6] lib/base64: Add support for multiple variants

Guan-Chun Wu
2025-11-14T06:00:52Z

From: Kuan-Wei Chiu <visitorckw@gmail.com>

Extend the base64 API to support multiple variants (standard, URL-safe,
and IMAP) as defined in RFC 4648 and RFC 3501. The API now takes a
variant parameter and an option to control padding. Update NVMe auth
code to use the new interface with BASE64_STD.

Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com>
Co-developed-by: Guan-Chun Wu <409411716@gms.tku.edu.tw>
Signed-off-by: Guan-Chun Wu <409411716@gms.tku.edu.tw>
---
drivers/nvme/common/auth.c | 4 +--
include/linux/base64.h | 10 ++++--
lib/base64.c | 62 ++++++++++++++++++++++----------------
3 files changed, 46 insertions(+), 30 deletions(-)

diff --git a/drivers/nvme/common/auth.c b/drivers/nvme/common/auth.c
index 1f51fbebd9fa..e07e7d4bf8b6 100644
--- a/drivers/nvme/common/auth.c
+++ b/drivers/nvme/common/auth.c
@@ -178,7 +178,7 @@ struct nvme_dhchap_key *nvme_auth_extract_key(unsigned char *secret,
if (!key)
return ERR_PTR(-ENOMEM);

- key_len = base64_decode(secret, allocated_len, key->key);
+ key_len = base64_decode(secret, allocated_len, key->key, true, BASE64_STD);
if (key_len < 0) {
pr_debug("base64 key decoding error %d\n",
key_len);
@@ -663,7 +663,7 @@ int nvme_auth_generate_digest(u8 hmac_id, u8 *psk, size_t psk_len,
if (ret)
goto out_free_digest;

- ret = base64_encode(digest, digest_len, enc);
+ ret = base64_encode(digest, digest_len, enc, true, BASE64_STD);
if (ret < hmac_len) {
ret = -ENOKEY;
goto out_free_digest;
diff --git a/include/linux/base64.h b/include/linux/base64.h
index 660d4cb1ef31..a2c6c9222da3 100644
--- a/include/linux/base64.h
+++ b/include/linux/base64.h
@@ -8,9 +8,15 @@

#include <linux/types.h>

+enum base64_variant {
+ BASE64_STD, /* RFC 4648 (standard) */
+ BASE64_URLSAFE, /* RFC 4648 (base64url) */
+ BASE64_IMAP, /* RFC 3501 */
+};
+
#define BASE64_CHARS(nbytes) DIV_ROUND_UP((nbytes) * 4, 3)

-int base64_encode(const u8 *src, int len, char *dst);
-int base64_decode(const char *src, int len, u8 *dst);
+int base64_encode(const u8 *src, int len, char *dst, bool padding, enum base64_variant variant);
+int base64_decode(const char *src, int len, u8 *dst, bool padding, enum base64_variant variant);

#endif /* _LINUX_BASE64_H */
diff --git a/lib/base64.c b/lib/base64.c
index b736a7a431c5..a7c20a8e8e98 100644
--- a/lib/base64.c
+++ b/lib/base64.c
@@ -1,12 +1,12 @@
// SPDX-License-Identifier: GPL-2.0
/*
- * base64.c - RFC4648-compliant base64 encoding
+ * base64.c - Base64 with support for multiple variants
*
* Copyright (c) 2020 Hannes Reinecke, SUSE
*
* Based on the base64url routines from fs/crypto/fname.c
- * (which are using the URL-safe base64 encoding),
- * modified to use the standard coding table from RFC4648 section 4.
+ * (which are using the URL-safe Base64 encoding),
+ * modified to support multiple Base64 variants.
*/

#include <linux/kernel.h>
@@ -15,26 +15,31 @@
#include <linux/string.h>
#include <linux/base64.h>

-static const char base64_table[65] =
- "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
+static const char base64_tables[][65] = {
+ [BASE64_STD] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/",
+ [BASE64_URLSAFE] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_",
+ [BASE64_IMAP] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+,",
+};

/**
- * base64_encode() - base64-encode some binary data
+ * base64_encode() - Base64-encode some binary data
* @src: the binary data to encode
* @srclen: the length of @src in bytes
- * @dst: (output) the base64-encoded string. Not NUL-terminated.
+ * @dst: (output) the Base64-encoded string. Not NUL-terminated.
+ * @padding: whether to append '=' padding characters
+ * @variant: which base64 variant to use
*
- * Encodes data using base64 encoding, i.e. the "Base 64 Encoding" specified
- * by RFC 4648, including the '='-padding.
+ * Encodes data using the selected Base64 variant.
*
- * Return: the length of the resulting base64-encoded string in bytes.
+ * Return: the length of the resulting Base64-encoded string in bytes.
*/
-int base64_encode(const u8 *src, int srclen, char *dst)
+int base64_encode(const u8 *src, int srclen, char *dst, bool padding, enum base64_variant variant)
{
u32 ac = 0;
int bits = 0;
int i;
char *cp = dst;
+ const char *base64_table = base64_tables[variant];

for (i = 0; i < srclen; i++) {
ac = (ac << 8) | src[i];
@@ -48,44 +53,49 @@ int base64_encode(const u8 *src, int srclen, char *dst)
*cp++ = base64_table[(ac << (6 - bits)) & 0x3f];
bits -= 6;
}
- while (bits < 0) {
- *cp++ = '=';
- bits += 2;
+ if (padding) {
+ while (bits < 0) {
+ *cp++ = '=';
+ bits += 2;
+ }
}
return cp - dst;
}
EXPORT_SYMBOL_GPL(base64_encode);

/**
- * base64_decode() - base64-decode a string
+ * base64_decode() - Base64-decode a string
* @src: the string to decode. Doesn't need to be NUL-terminated.
* @srclen: the length of @src in bytes
* @dst: (output) the decoded binary data
+ * @padding: whether to append '=' padding characters
+ * @variant: which base64 variant to use
*
- * Decodes a string using base64 encoding, i.e. the "Base 64 Encoding"
- * specified by RFC 4648, including the '='-padding.
+ * Decodes a string using the selected Base64 variant.
*
* This implementation hasn't been optimized for performance.
*
* Return: the length of the resulting decoded binary data in bytes,
- * or -1 if the string isn't a valid base64 string.
+ * or -1 if the string isn't a valid Base64 string.
*/
-int base64_decode(const char *src, int srclen, u8 *dst)
+int base64_decode(const char *src, int srclen, u8 *dst, bool padding, enum base64_variant variant)
{
u32 ac = 0;
int bits = 0;
int i;
u8 *bp = dst;
+ const char *base64_table = base64_tables[variant];

for (i = 0; i < srclen; i++) {
const char *p = strchr(base64_table, src[i]);
-
- if (src[i] == '=') {
- ac = (ac << 6);
- bits += 6;
- if (bits >= 8)
- bits -= 8;
- continue;
+ if (padding) {
+ if (src[i] == '=') {
+ ac = (ac << 6);
+ bits += 6;
+ if (bits >= 8)
+ bits -= 8;
+ continue;
+ }
}
if (p == NULL || src[i] == 0)
return -1;
--
2.34.1