From 52f72d298abd81a6102ddddf2fff4918e4b077ce Mon Sep 17 00:00:00 2001
From: Michael Brown
Date: Tue, 25 Oct 2022 12:59:06 +0100
Subject: [crypto] Expose null crypto algorithm methods for reuse

Signed-off-by: Michael Brown <mcb30@ipxe.org>
---
 src/crypto/arc4.c | 8 +-------
 1 file changed, 1 insertion(+), 7 deletions(-)

(limited to 'src/crypto/arc4.c')

diff --git a/src/crypto/arc4.c b/src/crypto/arc4.c
index 91a732019..0dba2fc59 100644
--- a/src/crypto/arc4.c
+++ b/src/crypto/arc4.c
@@ -96,12 +96,6 @@ static void arc4_xor ( void *ctxv, const void *srcv, void *dstv,
 	ctx->j = j;
 }
 
-static void arc4_setiv ( void *ctx __unused, const void *iv __unused )
-{
-	/* ARC4 does not use a fixed-length IV */
-}
-
-
 /**
  * Perform ARC4 encryption or decryption, skipping initial keystream bytes
  *
@@ -126,7 +120,7 @@ struct cipher_algorithm arc4_algorithm = {
 	.ctxsize = ARC4_CTX_SIZE,
 	.blocksize = 1,
 	.setkey = arc4_setkey,
-	.setiv = arc4_setiv,
+	.setiv = cipher_null_setiv,
 	.encrypt = arc4_xor,
 	.decrypt = arc4_xor,
 };
-- 
cgit v1.2.3-55-g7522


From da81214cec87201dc18c0ce71224367e13a6edfb Mon Sep 17 00:00:00 2001
From: Michael Brown
Date: Mon, 24 Oct 2022 19:20:41 +0100
Subject: [crypto] Add concept of authentication tag to cipher algorithms

Some ciphers (such as GCM) support the concept of a tag that can be
used to authenticate the encrypted data.  Add a cipher method for
generating an authentication tag.

Signed-off-by: Michael Brown <mcb30@ipxe.org>
---
 src/crypto/aes.c          |  2 ++
 src/crypto/arc4.c         |  2 ++
 src/crypto/crypto_null.c  |  6 ++++++
 src/include/ipxe/cbc.h    |  2 ++
 src/include/ipxe/crypto.h | 18 ++++++++++++++++++
 src/include/ipxe/ecb.h    |  2 ++
 src/tests/aes_test.c      | 12 ++++++------
 src/tests/cipher_test.c   | 14 ++++++++++++++
 src/tests/cipher_test.h   | 13 ++++++++++++-
 9 files changed, 64 insertions(+), 7 deletions(-)

(limited to 'src/crypto/arc4.c')

diff --git a/src/crypto/aes.c b/src/crypto/aes.c
index d7393285f..4a7668b6b 100644
--- a/src/crypto/aes.c
+++ b/src/crypto/aes.c
@@ -783,10 +783,12 @@ struct cipher_algorithm aes_algorithm = {
 	.name = "aes",
 	.ctxsize = sizeof ( struct aes_context ),
 	.blocksize = AES_BLOCKSIZE,
+	.authsize = 0,
 	.setkey = aes_setkey,
 	.setiv = cipher_null_setiv,
 	.encrypt = aes_encrypt,
 	.decrypt = aes_decrypt,
+	.auth = cipher_null_auth,
 };
 
 /* AES in Electronic Codebook mode */
diff --git a/src/crypto/arc4.c b/src/crypto/arc4.c
index 0dba2fc59..4d98abead 100644
--- a/src/crypto/arc4.c
+++ b/src/crypto/arc4.c
@@ -119,8 +119,10 @@ struct cipher_algorithm arc4_algorithm = {
 	.name = "ARC4",
 	.ctxsize = ARC4_CTX_SIZE,
 	.blocksize = 1,
+	.authsize = 0,
 	.setkey = arc4_setkey,
 	.setiv = cipher_null_setiv,
 	.encrypt = arc4_xor,
 	.decrypt = arc4_xor,
+	.auth = cipher_null_auth,
 };
diff --git a/src/crypto/crypto_null.c b/src/crypto/crypto_null.c
index ef6041b5b..26cfbfc4e 100644
--- a/src/crypto/crypto_null.c
+++ b/src/crypto/crypto_null.c
@@ -76,14 +76,20 @@ void cipher_null_decrypt ( void *ctx __unused, const void *src, void *dst,
 	memcpy ( dst, src, len );
 }
 
+void cipher_null_auth ( void *ctx __unused, void *auth __unused ) {
+	/* Do nothing */
+}
+
 struct cipher_algorithm cipher_null = {
 	.name = "null",
 	.ctxsize = 0,
 	.blocksize = 1,
+	.authsize = 0,
 	.setkey = cipher_null_setkey,
 	.setiv = cipher_null_setiv,
 	.encrypt = cipher_null_encrypt,
 	.decrypt = cipher_null_decrypt,
+	.auth = cipher_null_auth,
 };
 
 int pubkey_null_init ( void *ctx __unused, const void *key __unused,
diff --git a/src/include/ipxe/cbc.h b/src/include/ipxe/cbc.h
index 5c8740365..eead045ed 100644
--- a/src/include/ipxe/cbc.h
+++ b/src/include/ipxe/cbc.h
@@ -95,10 +95,12 @@ struct cipher_algorithm _cbc_cipher = {					\
 	.name		= #_cbc_name,					\
 	.ctxsize	= sizeof ( struct _cbc_name ## _context ),	\
 	.blocksize	= _blocksize,					\
+	.authsize	= 0,						\
 	.setkey		= _cbc_name ## _setkey,				\
 	.setiv		= _cbc_name ## _setiv,				\
 	.encrypt	= _cbc_name ## _encrypt,			\
 	.decrypt	= _cbc_name ## _decrypt,			\
+	.auth		= cipher_null_auth,				\
 };
 
 #endif /* _IPXE_CBC_H */
diff --git a/src/include/ipxe/crypto.h b/src/include/ipxe/crypto.h
index d41448024..e807aeb52 100644
--- a/src/include/ipxe/crypto.h
+++ b/src/include/ipxe/crypto.h
@@ -52,6 +52,8 @@ struct cipher_algorithm {
 	size_t ctxsize;
 	/** Block size */
 	size_t blocksize;
+	/** Authentication tag size */
+	size_t authsize;
 	/** Set key
 	 *
 	 * @v ctx	Context
@@ -89,6 +91,12 @@ struct cipher_algorithm {
 	 */
 	void ( * decrypt ) ( void *ctx, const void *src, void *dst,
 			     size_t len );
+	/** Generate authentication tag
+	 *
+	 * @v ctx	Context
+	 * @v auth	Authentication tag
+	 */
+	void ( * auth ) ( void *ctx, void *auth );
 };
 
 /** A public key algorithm */
@@ -215,10 +223,19 @@ static inline void cipher_decrypt ( struct cipher_algorithm *cipher,
 	cipher_decrypt ( (cipher), (ctx), (src), (dst), (len) );	\
 	} while ( 0 )
 
+static inline void cipher_auth ( struct cipher_algorithm *cipher, void *ctx,
+				 void *auth ) {
+	cipher->auth ( ctx, auth );
+}
+
 static inline int is_stream_cipher ( struct cipher_algorithm *cipher ) {
 	return ( cipher->blocksize == 1 );
 }
 
+static inline int is_auth_cipher ( struct cipher_algorithm *cipher ) {
+	return cipher->authsize;
+}
+
 static inline int pubkey_init ( struct pubkey_algorithm *pubkey, void *ctx,
 				const void *key, size_t key_len ) {
 	return pubkey->init ( ctx, key, key_len );
@@ -274,6 +291,7 @@ extern void cipher_null_encrypt ( void *ctx, const void *src, void *dst,
 				  size_t len );
 extern void cipher_null_decrypt ( void *ctx, const void *src, void *dst,
 				  size_t len );
+extern void cipher_null_auth ( void *ctx, void *auth );
 
 extern int pubkey_null_init ( void *ctx, const void *key, size_t key_len );
 extern size_t pubkey_null_max_len ( void *ctx );
diff --git a/src/include/ipxe/ecb.h b/src/include/ipxe/ecb.h
index 6c40c6126..1d2ebf716 100644
--- a/src/include/ipxe/ecb.h
+++ b/src/include/ipxe/ecb.h
@@ -47,10 +47,12 @@ struct cipher_algorithm _ecb_cipher = {					\
 	.name		= #_ecb_name,					\
 	.ctxsize	= sizeof ( _raw_context ),			\
 	.blocksize	= _blocksize,					\
+	.authsize	= 0,						\
 	.setkey		= _ecb_name ## _setkey,				\
 	.setiv		= _ecb_name ## _setiv,				\
 	.encrypt	= _ecb_name ## _encrypt,			\
 	.decrypt	= _ecb_name ## _decrypt,			\
+	.auth		= cipher_null_auth,				\
 };
 
 #endif /* _IPXE_ECB_H */
diff --git a/src/tests/aes_test.c b/src/tests/aes_test.c
index e7201fca6..be119c8d8 100644
--- a/src/tests/aes_test.c
+++ b/src/tests/aes_test.c
@@ -94,7 +94,7 @@ CIPHER_TEST ( aes_128_ecb, &aes_ecb_algorithm,
 		     0x43, 0xb1, 0xcd, 0x7f, 0x59, 0x8e, 0xce, 0x23,
 		     0x88, 0x1b, 0x00, 0xe3, 0xed, 0x03, 0x06, 0x88,
 		     0x7b, 0x0c, 0x78, 0x5e, 0x27, 0xe8, 0xad, 0x3f,
-		     0x82, 0x23, 0x20, 0x71, 0x04, 0x72, 0x5d, 0xd4 ) );
+		     0x82, 0x23, 0x20, 0x71, 0x04, 0x72, 0x5d, 0xd4 ), AUTH() );
 
 /** AES-128-CBC */
 CIPHER_TEST ( aes_128_cbc, &aes_cbc_algorithm,
@@ -106,7 +106,7 @@ CIPHER_TEST ( aes_128_cbc, &aes_cbc_algorithm,
 		     0x73, 0xbe, 0xd6, 0xb8, 0xe3, 0xc1, 0x74, 0x3b,
 		     0x71, 0x16, 0xe6, 0x9e, 0x22, 0x22, 0x95, 0x16,
 		     0x3f, 0xf1, 0xca, 0xa1, 0x68, 0x1f, 0xac, 0x09,
-		     0x12, 0x0e, 0xca, 0x30, 0x75, 0x86, 0xe1, 0xa7 ) );
+		     0x12, 0x0e, 0xca, 0x30, 0x75, 0x86, 0xe1, 0xa7 ), AUTH() );
 
 /** AES-192-ECB (same test as AES-192-Core) */
 CIPHER_TEST ( aes_192_ecb, &aes_ecb_algorithm,
@@ -118,7 +118,7 @@ CIPHER_TEST ( aes_192_ecb, &aes_ecb_algorithm,
 		     0xef, 0x7a, 0xfd, 0x22, 0x70, 0xe2, 0xe6, 0x0a,
 		     0xdc, 0xe0, 0xba, 0x2f, 0xac, 0xe6, 0x44, 0x4e,
 		     0x9a, 0x4b, 0x41, 0xba, 0x73, 0x8d, 0x6c, 0x72,
-		     0xfb, 0x16, 0x69, 0x16, 0x03, 0xc1, 0x8e, 0x0e ) );
+		     0xfb, 0x16, 0x69, 0x16, 0x03, 0xc1, 0x8e, 0x0e ), AUTH() );
 
 /** AES-192-CBC */
 CIPHER_TEST ( aes_192_cbc, &aes_cbc_algorithm,
@@ -130,7 +130,7 @@ CIPHER_TEST ( aes_192_cbc, &aes_cbc_algorithm,
 		     0x57, 0x1b, 0x24, 0x20, 0x12, 0xfb, 0x7a, 0xe0,
 		     0x7f, 0xa9, 0xba, 0xac, 0x3d, 0xf1, 0x02, 0xe0,
 		     0x08, 0xb0, 0xe2, 0x79, 0x88, 0x59, 0x88, 0x81,
-		     0xd9, 0x20, 0xa9, 0xe6, 0x4f, 0x56, 0x15, 0xcd ) );
+		     0xd9, 0x20, 0xa9, 0xe6, 0x4f, 0x56, 0x15, 0xcd ), AUTH() );
 
 /** AES-256-ECB (same test as AES-256-Core) */
 CIPHER_TEST ( aes_256_ecb, &aes_ecb_algorithm,
@@ -142,7 +142,7 @@ CIPHER_TEST ( aes_256_ecb, &aes_ecb_algorithm,
 		     0xb6, 0xed, 0x21, 0xb9, 0x9c, 0xa6, 0xf4, 0xf9,
 		     0xf1, 0x53, 0xe7, 0xb1, 0xbe, 0xaf, 0xed, 0x1d,
 		     0x23, 0x30, 0x4b, 0x7a, 0x39, 0xf9, 0xf3, 0xff,
-		     0x06, 0x7d, 0x8d, 0x8f, 0x9e, 0x24, 0xec, 0xc7 ) );
+		     0x06, 0x7d, 0x8d, 0x8f, 0x9e, 0x24, 0xec, 0xc7 ), AUTH() );
 
 /** AES-256-CBC */
 CIPHER_TEST ( aes_256_cbc, &aes_cbc_algorithm,
@@ -154,7 +154,7 @@ CIPHER_TEST ( aes_256_cbc, &aes_cbc_algorithm,
 		     0x39, 0xf2, 0x33, 0x69, 0xa9, 0xd9, 0xba, 0xcf,
 		     0xa5, 0x30, 0xe2, 0x63, 0x04, 0x23, 0x14, 0x61,
 		     0xb2, 0xeb, 0x05, 0xe2, 0xc3, 0x9b, 0xe9, 0xfc,
-		     0xda, 0x6c, 0x19, 0x07, 0x8c, 0x6a, 0x9d, 0x1b ) );
+		     0xda, 0x6c, 0x19, 0x07, 0x8c, 0x6a, 0x9d, 0x1b ), AUTH() );
 
 /**
  * Perform AES self-test
diff --git a/src/tests/cipher_test.c b/src/tests/cipher_test.c
index c49b4b69b..cc732c2e0 100644
--- a/src/tests/cipher_test.c
+++ b/src/tests/cipher_test.c
@@ -57,6 +57,7 @@ void cipher_encrypt_okx ( struct cipher_test *test, const char *file,
 	size_t len = test->len;
 	uint8_t ctx[cipher->ctxsize];
 	uint8_t ciphertext[len];
+	uint8_t auth[cipher->authsize];
 
 	/* Initialise cipher */
 	okx ( cipher_setkey ( cipher, ctx, test->key, test->key_len ) == 0,
@@ -65,6 +66,7 @@ void cipher_encrypt_okx ( struct cipher_test *test, const char *file,
 
 	/* Process additional data, if applicable */
 	if ( test->additional_len ) {
+		okx ( is_auth_cipher ( cipher ), file, line );
 		cipher_encrypt ( cipher, ctx, test->additional, NULL,
 				 test->additional_len );
 	}
@@ -74,6 +76,11 @@ void cipher_encrypt_okx ( struct cipher_test *test, const char *file,
 
 	/* Compare against expected ciphertext */
 	okx ( memcmp ( ciphertext, test->ciphertext, len ) == 0, file, line );
+
+	/* Check authentication tag */
+	okx ( cipher->authsize == test->auth_len, file, line );
+	cipher_auth ( cipher, ctx, auth );
+	okx ( memcmp ( auth, test->auth, test->auth_len ) == 0, file, line );
 }
 
 /**
@@ -89,6 +96,7 @@ void cipher_decrypt_okx ( struct cipher_test *test, const char *file,
 	size_t len = test->len;
 	uint8_t ctx[cipher->ctxsize];
 	uint8_t plaintext[len];
+	uint8_t auth[cipher->authsize];
 
 	/* Initialise cipher */
 	okx ( cipher_setkey ( cipher, ctx, test->key, test->key_len ) == 0,
@@ -97,6 +105,7 @@ void cipher_decrypt_okx ( struct cipher_test *test, const char *file,
 
 	/* Process additional data, if applicable */
 	if ( test->additional_len ) {
+		okx ( is_auth_cipher ( cipher ), file, line );
 		cipher_decrypt ( cipher, ctx, test->additional, NULL,
 				 test->additional_len );
 	}
@@ -106,6 +115,11 @@ void cipher_decrypt_okx ( struct cipher_test *test, const char *file,
 
 	/* Compare against expected plaintext */
 	okx ( memcmp ( plaintext, test->plaintext, len ) == 0, file, line );
+
+	/* Check authentication tag */
+	okx ( cipher->authsize == test->auth_len, file, line );
+	cipher_auth ( cipher, ctx, auth );
+	okx ( memcmp ( auth, test->auth, test->auth_len ) == 0, file, line );
 }
 
 /**
diff --git a/src/tests/cipher_test.h b/src/tests/cipher_test.h
index 4139a7788..519d12e8d 100644
--- a/src/tests/cipher_test.h
+++ b/src/tests/cipher_test.h
@@ -35,6 +35,10 @@ struct cipher_test {
 	const void *ciphertext;
 	/** Length of text */
 	size_t len;
+	/** Authentication tag */
+	const void *auth;
+	/** Length of authentication tag */
+	size_t auth_len;
 };
 
 /** Define inline key */
@@ -52,6 +56,9 @@ struct cipher_test {
 /** Define inline ciphertext data */
 #define CIPHERTEXT(...) { __VA_ARGS__ }
 
+/** Define inline authentication tag */
+#define AUTH(...) { __VA_ARGS__ }
+
 /**
  * Define a cipher test
  *
@@ -62,16 +69,18 @@ struct cipher_test {
  * @v ADDITIONAL	Additional data
  * @v PLAINTEXT		Plaintext
  * @v CIPHERTEXT	Ciphertext
+ * @v AUTH		Authentication tag
  * @ret test		Cipher test
  */
 #define CIPHER_TEST( name, CIPHER, KEY, IV, ADDITIONAL, PLAINTEXT,	\
-		     CIPHERTEXT )					\
+		     CIPHERTEXT, AUTH )					\
 	static const uint8_t name ## _key [] = KEY;			\
 	static const uint8_t name ## _iv [] = IV;			\
 	static const uint8_t name ## _additional [] = ADDITIONAL;	\
 	static const uint8_t name ## _plaintext [] = PLAINTEXT;		\
 	static const uint8_t name ## _ciphertext			\
 		[ sizeof ( name ## _plaintext ) ] = CIPHERTEXT;		\
+	static const uint8_t name ## _auth [] = AUTH;			\
 	static struct cipher_test name = {				\
 		.cipher = CIPHER,					\
 		.key = name ## _key,					\
@@ -83,6 +92,8 @@ struct cipher_test {
 		.plaintext = name ## _plaintext,			\
 		.ciphertext = name ## _ciphertext,			\
 		.len = sizeof ( name ## _plaintext ),			\
+		.auth = name ## _auth,					\
+		.auth_len = sizeof ( name ## _auth ),			\
 	}
 
 extern void cipher_encrypt_okx ( struct cipher_test *test, const char *file,
-- 
cgit v1.2.3-55-g7522


From 30243ad73957a2e1cc4aedc3f23be66cdf399f00 Mon Sep 17 00:00:00 2001
From: Michael Brown
Date: Fri, 28 Oct 2022 16:27:10 +0100
Subject: [crypto] Add concept of cipher alignment size

The GCM cipher mode of operation (in common with other counter-based
modes of operation) has a notion of blocksize that does not neatly
fall into our current abstraction: it does operate in 16-byte blocks
but allows for an arbitrary overall data length (i.e. the final block
may be incomplete).

Model this by adding a concept of alignment size.  Each call to
encrypt() or decrypt() must begin at a multiple of the alignment size
from the start of the data stream.  This allows us to model GCM by
using a block size of 1 byte and an alignment size of 16 bytes.

As a side benefit, this same concept allows us to neatly model the
fact that raw AES can encrypt only a single 16-byte block, by
specifying an alignment size of zero on this cipher.

Signed-off-by: Michael Brown <mcb30@ipxe.org>
---
 src/crypto/aes.c          |  1 +
 src/crypto/arc4.c         |  1 +
 src/crypto/crypto_null.c  |  1 +
 src/include/ipxe/cbc.h    |  1 +
 src/include/ipxe/crypto.h | 18 +++++++++++++++++-
 src/include/ipxe/ecb.h    |  1 +
 src/include/ipxe/gcm.h    |  1 +
 src/tests/cipher_test.c   | 10 ++++++++++
 8 files changed, 33 insertions(+), 1 deletion(-)

(limited to 'src/crypto/arc4.c')

diff --git a/src/crypto/aes.c b/src/crypto/aes.c
index aeeaa1d2c..5200e7760 100644
--- a/src/crypto/aes.c
+++ b/src/crypto/aes.c
@@ -784,6 +784,7 @@ struct cipher_algorithm aes_algorithm = {
 	.name = "aes",
 	.ctxsize = sizeof ( struct aes_context ),
 	.blocksize = AES_BLOCKSIZE,
+	.alignsize = 0,
 	.authsize = 0,
 	.setkey = aes_setkey,
 	.setiv = cipher_null_setiv,
diff --git a/src/crypto/arc4.c b/src/crypto/arc4.c
index 4d98abead..3b6adec19 100644
--- a/src/crypto/arc4.c
+++ b/src/crypto/arc4.c
@@ -119,6 +119,7 @@ struct cipher_algorithm arc4_algorithm = {
 	.name = "ARC4",
 	.ctxsize = ARC4_CTX_SIZE,
 	.blocksize = 1,
+	.alignsize = 1,
 	.authsize = 0,
 	.setkey = arc4_setkey,
 	.setiv = cipher_null_setiv,
diff --git a/src/crypto/crypto_null.c b/src/crypto/crypto_null.c
index 26cfbfc4e..0ad463c3e 100644
--- a/src/crypto/crypto_null.c
+++ b/src/crypto/crypto_null.c
@@ -84,6 +84,7 @@ struct cipher_algorithm cipher_null = {
 	.name = "null",
 	.ctxsize = 0,
 	.blocksize = 1,
+	.alignsize = 1,
 	.authsize = 0,
 	.setkey = cipher_null_setkey,
 	.setiv = cipher_null_setiv,
diff --git a/src/include/ipxe/cbc.h b/src/include/ipxe/cbc.h
index eead045ed..382fc9036 100644
--- a/src/include/ipxe/cbc.h
+++ b/src/include/ipxe/cbc.h
@@ -95,6 +95,7 @@ struct cipher_algorithm _cbc_cipher = {					\
 	.name		= #_cbc_name,					\
 	.ctxsize	= sizeof ( struct _cbc_name ## _context ),	\
 	.blocksize	= _blocksize,					\
+	.alignsize	= _blocksize,					\
 	.authsize	= 0,						\
 	.setkey		= _cbc_name ## _setkey,				\
 	.setiv		= _cbc_name ## _setiv,				\
diff --git a/src/include/ipxe/crypto.h b/src/include/ipxe/crypto.h
index 842f2f633..ba09c9468 100644
--- a/src/include/ipxe/crypto.h
+++ b/src/include/ipxe/crypto.h
@@ -51,8 +51,24 @@ struct cipher_algorithm {
 	const char *name;
 	/** Context size */
 	size_t ctxsize;
-	/** Block size */
+	/** Block size
+	 *
+	 * Every call to encrypt() or decrypt() must be for a multiple
+	 * of this size.
+	 */
 	size_t blocksize;
+	/** Alignment size
+	 *
+	 * Every call to encrypt() or decrypt() must begin at a
+	 * multiple of this offset from the start of the stream.
+	 * (Equivalently: all but the last call to encrypt() or
+	 * decrypt() must be for a multiple of this size.)
+	 *
+	 * For ciphers supporting additional data, the main data
+	 * stream and additional data stream are both considered to
+	 * begin at offset zero.
+	 */
+	size_t alignsize;
 	/** Authentication tag size */
 	size_t authsize;
 	/** Set key
diff --git a/src/include/ipxe/ecb.h b/src/include/ipxe/ecb.h
index 1d2ebf716..db22d996d 100644
--- a/src/include/ipxe/ecb.h
+++ b/src/include/ipxe/ecb.h
@@ -47,6 +47,7 @@ struct cipher_algorithm _ecb_cipher = {					\
 	.name		= #_ecb_name,					\
 	.ctxsize	= sizeof ( _raw_context ),			\
 	.blocksize	= _blocksize,					\
+	.alignsize	= _blocksize,					\
 	.authsize	= 0,						\
 	.setkey		= _ecb_name ## _setkey,				\
 	.setiv		= _ecb_name ## _setiv,				\
diff --git a/src/include/ipxe/gcm.h b/src/include/ipxe/gcm.h
index 658685486..d93eecd8e 100644
--- a/src/include/ipxe/gcm.h
+++ b/src/include/ipxe/gcm.h
@@ -121,6 +121,7 @@ struct cipher_algorithm _gcm_cipher = {					\
 	.name		= #_gcm_name,					\
 	.ctxsize	= sizeof ( struct _gcm_name ## _context ),	\
 	.blocksize	= 1,						\
+	.alignsize	= sizeof ( union gcm_block ),			\
 	.authsize	= sizeof ( union gcm_block ),			\
 	.setkey		= _gcm_name ## _setkey,				\
 	.setiv		= _gcm_name ## _setiv,				\
diff --git a/src/tests/cipher_test.c b/src/tests/cipher_test.c
index cc732c2e0..2ead3c827 100644
--- a/src/tests/cipher_test.c
+++ b/src/tests/cipher_test.c
@@ -131,8 +131,18 @@ void cipher_decrypt_okx ( struct cipher_test *test, const char *file,
  */
 void cipher_okx ( struct cipher_test *test, const char *file,
 		  unsigned int line ) {
+	struct cipher_algorithm *cipher = test->cipher;
+	size_t len = test->len;
 
+	/* Sanity checks */
+	okx ( cipher->blocksize != 0, file, line );
+	okx ( ( len % cipher->blocksize ) == 0, file, line );
+	okx ( ( cipher->alignsize % cipher->blocksize ) == 0, file, line );
+
+	/* Report encryption test result */
 	cipher_encrypt_okx ( test, file, line );
+
+	/* Report decryption test result */
 	cipher_decrypt_okx ( test, file, line );
 }
 
-- 
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