lib/crypto: md5: Add MD5 and HMAC-MD5 library functions

Add library functions for MD5, including HMAC support.  The MD5
implementation is derived from crypto/md5.c.  This closely mirrors the
corresponding SHA-1 and SHA-2 changes.

Like SHA-1 and SHA-2, support for architecture-optimized MD5
implementations is included.  I originally proposed dropping those, but
unfortunately there is an AF_ALG user of the PowerPC MD5 code
(https://lore.kernel.org/r/c4191597-341d-4fd7-bc3d-13daf7666c41@csgroup.eu/),
and dropping that code would be viewed as a performance regression.  We
don't add new software algorithm implementations purely for AF_ALG, as
escalating to kernel mode merely to do calculations that could be done
in userspace is inefficient and is completely the wrong design.  But
since this one already existed, it gets grandfathered in for now.  An
objection was also raised to dropping the SPARC64 MD5 code because it
utilizes the CPU's direct support for MD5, although it remains unclear
that anyone is using that.  Regardless, we'll keep these around for now.

Note that while MD5 is a legacy algorithm that is vulnerable to
practical collision attacks, it still has various in-kernel users that
implement legacy protocols.  Switching to a simple library API, which is
the way the code should have been organized originally, will greatly
simplify their code.  For example:

    MD5:
        drivers/md/dm-crypt.c (for lmk IV generation)
        fs/nfsd/nfs4recover.c
        fs/ecryptfs/
        fs/smb/client/
        net/{ipv4,ipv6}/ (for TCP-MD5 signatures)

    HMAC-MD5:
        fs/smb/client/
        fs/smb/server/

(Also net/sctp/ if it continues using HMAC-MD5 for cookie generation.
However, that use case has the flexibility to upgrade to a more modern
algorithm, which I'll be proposing instead.)

As usual, the "md5" and "hmac(md5)" crypto_shash algorithms will also be
reimplemented on top of these library functions.  For "hmac(md5)" this
will provide a faster, more streamlined implementation.

Link: https://lore.kernel.org/r/20250805222855.10362-2-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>

1 files changed, 180 insertions, 1 deletions

diff --git a/include/crypto/md5.h b/include/crypto/md5.h
index 28ee533a0507..c9aa5c3abc53 100644
--- a/include/crypto/md5.h
+++ b/include/crypto/md5.h
@@ -7,6 +7,7 @@
 
 #define MD5_DIGEST_SIZE		16
 #define MD5_HMAC_BLOCK_SIZE	64
+#define MD5_BLOCK_SIZE		64
 #define MD5_BLOCK_WORDS		16
 #define MD5_HASH_WORDS		4
 #define MD5_STATE_SIZE		24
@@ -27,4 +28,182 @@ struct md5_state {
 	u32 block[MD5_BLOCK_WORDS];
 };
 
-#endif
+/* State for the MD5 compression function */
+struct md5_block_state {
+	u32 h[MD5_HASH_WORDS];
+};
+
+/**
+ * struct md5_ctx - Context for hashing a message with MD5
+ * @state: the compression function state
+ * @bytecount: number of bytes processed so far
+ * @buf: partial block buffer; bytecount % MD5_BLOCK_SIZE bytes are valid
+ */
+struct md5_ctx {
+	struct md5_block_state state;
+	u64 bytecount;
+	u8 buf[MD5_BLOCK_SIZE] __aligned(__alignof__(__le64));
+};
+
+/**
+ * md5_init() - Initialize an MD5 context for a new message
+ * @ctx: the context to initialize
+ *
+ * If you don't need incremental computation, consider md5() instead.
+ *
+ * Context: Any context.
+ */
+void md5_init(struct md5_ctx *ctx);
+
+/**
+ * md5_update() - Update an MD5 context with message data
+ * @ctx: the context to update; must have been initialized
+ * @data: the message data
+ * @len: the data length in bytes
+ *
+ * This can be called any number of times.
+ *
+ * Context: Any context.
+ */
+void md5_update(struct md5_ctx *ctx, const u8 *data, size_t len);
+
+/**
+ * md5_final() - Finish computing an MD5 message digest
+ * @ctx: the context to finalize; must have been initialized
+ * @out: (output) the resulting MD5 message digest
+ *
+ * After finishing, this zeroizes @ctx.  So the caller does not need to do it.
+ *
+ * Context: Any context.
+ */
+void md5_final(struct md5_ctx *ctx, u8 out[MD5_DIGEST_SIZE]);
+
+/**
+ * md5() - Compute MD5 message digest in one shot
+ * @data: the message data
+ * @len: the data length in bytes
+ * @out: (output) the resulting MD5 message digest
+ *
+ * Context: Any context.
+ */
+void md5(const u8 *data, size_t len, u8 out[MD5_DIGEST_SIZE]);
+
+/**
+ * struct hmac_md5_key - Prepared key for HMAC-MD5
+ * @istate: private
+ * @ostate: private
+ */
+struct hmac_md5_key {
+	struct md5_block_state istate;
+	struct md5_block_state ostate;
+};
+
+/**
+ * struct hmac_md5_ctx - Context for computing HMAC-MD5 of a message
+ * @hash_ctx: private
+ * @ostate: private
+ */
+struct hmac_md5_ctx {
+	struct md5_ctx hash_ctx;
+	struct md5_block_state ostate;
+};
+
+/**
+ * hmac_md5_preparekey() - Prepare a key for HMAC-MD5
+ * @key: (output) the key structure to initialize
+ * @raw_key: the raw HMAC-MD5 key
+ * @raw_key_len: the key length in bytes.  All key lengths are supported.
+ *
+ * Note: the caller is responsible for zeroizing both the struct hmac_md5_key
+ * and the raw key once they are no longer needed.
+ *
+ * Context: Any context.
+ */
+void hmac_md5_preparekey(struct hmac_md5_key *key,
+			 const u8 *raw_key, size_t raw_key_len);
+
+/**
+ * hmac_md5_init() - Initialize an HMAC-MD5 context for a new message
+ * @ctx: (output) the HMAC context to initialize
+ * @key: the prepared HMAC key
+ *
+ * If you don't need incremental computation, consider hmac_md5() instead.
+ *
+ * Context: Any context.
+ */
+void hmac_md5_init(struct hmac_md5_ctx *ctx, const struct hmac_md5_key *key);
+
+/**
+ * hmac_md5_init_usingrawkey() - Initialize an HMAC-MD5 context for a new
+ *				  message, using a raw key
+ * @ctx: (output) the HMAC context to initialize
+ * @raw_key: the raw HMAC-MD5 key
+ * @raw_key_len: the key length in bytes.  All key lengths are supported.
+ *
+ * If you don't need incremental computation, consider hmac_md5_usingrawkey()
+ * instead.
+ *
+ * Context: Any context.
+ */
+void hmac_md5_init_usingrawkey(struct hmac_md5_ctx *ctx,
+			       const u8 *raw_key, size_t raw_key_len);
+
+/**
+ * hmac_md5_update() - Update an HMAC-MD5 context with message data
+ * @ctx: the HMAC context to update; must have been initialized
+ * @data: the message data
+ * @data_len: the data length in bytes
+ *
+ * This can be called any number of times.
+ *
+ * Context: Any context.
+ */
+static inline void hmac_md5_update(struct hmac_md5_ctx *ctx,
+				   const u8 *data, size_t data_len)
+{
+	md5_update(&ctx->hash_ctx, data, data_len);
+}
+
+/**
+ * hmac_md5_final() - Finish computing an HMAC-MD5 value
+ * @ctx: the HMAC context to finalize; must have been initialized
+ * @out: (output) the resulting HMAC-MD5 value
+ *
+ * After finishing, this zeroizes @ctx.  So the caller does not need to do it.
+ *
+ * Context: Any context.
+ */
+void hmac_md5_final(struct hmac_md5_ctx *ctx, u8 out[MD5_DIGEST_SIZE]);
+
+/**
+ * hmac_md5() - Compute HMAC-MD5 in one shot, using a prepared key
+ * @key: the prepared HMAC key
+ * @data: the message data
+ * @data_len: the data length in bytes
+ * @out: (output) the resulting HMAC-MD5 value
+ *
+ * If you're using the key only once, consider using hmac_md5_usingrawkey().
+ *
+ * Context: Any context.
+ */
+void hmac_md5(const struct hmac_md5_key *key,
+	      const u8 *data, size_t data_len, u8 out[MD5_DIGEST_SIZE]);
+
+/**
+ * hmac_md5_usingrawkey() - Compute HMAC-MD5 in one shot, using a raw key
+ * @raw_key: the raw HMAC-MD5 key
+ * @raw_key_len: the key length in bytes.  All key lengths are supported.
+ * @data: the message data
+ * @data_len: the data length in bytes
+ * @out: (output) the resulting HMAC-MD5 value
+ *
+ * If you're using the key multiple times, prefer to use hmac_md5_preparekey()
+ * followed by multiple calls to hmac_md5() instead.
+ *
+ * Context: Any context.
+ */
+void hmac_md5_usingrawkey(const u8 *raw_key, size_t raw_key_len,
+			  const u8 *data, size_t data_len,
+			  u8 out[MD5_DIGEST_SIZE]);
+
+#endif /* _CRYPTO_MD5_H */