[PATCH v4 09/14] crypto: arm/chacha - add XChaCha12 support

Eric Biggers
2018-11-17T01:28:58Z

Now that the 32-bit ARM NEON implementation of ChaCha20 and XChaCha20
has been refactored to support varying the number of rounds, add support
for XChaCha12. This is identical to XChaCha20 except for the number of
rounds, which is 12 instead of 20.

XChaCha12 is faster than XChaCha20 but has a lower security margin,
though still greater than AES-256's since the best known attacks make it
through only 7 rounds. See the patch "crypto: chacha - add XChaCha12
support" for more details about why we need XChaCha12 support.

Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
---
arch/arm/crypto/Kconfig | 2 +-
arch/arm/crypto/chacha-neon-glue.c | 21 ++++++++++++++++++++-
2 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/arch/arm/crypto/Kconfig b/arch/arm/crypto/Kconfig
index a08759c32cb9..59c674cf08ef 100644
--- a/arch/arm/crypto/Kconfig
+++ b/arch/arm/crypto/Kconfig
@@ -126,7 +126,7 @@ config CRYPTO_CRC32_ARM_CE
select CRYPTO_HASH

config CRYPTO_CHACHA20_NEON
- tristate "NEON accelerated ChaCha20 stream cipher algorithms"
+ tristate "NEON accelerated ChaCha stream cipher algorithms"
depends on KERNEL_MODE_NEON
select CRYPTO_BLKCIPHER
select CRYPTO_CHACHA20
diff --git a/arch/arm/crypto/chacha-neon-glue.c b/arch/arm/crypto/chacha-neon-glue.c
index 385557d38634..9d6fda81986d 100644
--- a/arch/arm/crypto/chacha-neon-glue.c
+++ b/arch/arm/crypto/chacha-neon-glue.c
@@ -1,5 +1,6 @@
/*
- * ChaCha20 (RFC7539) and XChaCha20 stream ciphers, NEON accelerated
+ * ARM NEON accelerated ChaCha and XChaCha stream ciphers,
+ * including ChaCha20 (RFC7539)
*
* Copyright (C) 2016 Linaro, Ltd. <ard.biesheuvel@linaro.org>
*
@@ -154,6 +155,22 @@ static struct skcipher_alg algs[] = {
.setkey = crypto_chacha20_setkey,
.encrypt = xchacha_neon,
.decrypt = xchacha_neon,
+ }, {
+ .base.cra_name = "xchacha12",
+ .base.cra_driver_name = "xchacha12-neon",
+ .base.cra_priority = 300,
+ .base.cra_blocksize = 1,
+ .base.cra_ctxsize = sizeof(struct chacha_ctx),
+ .base.cra_module = THIS_MODULE,
+
+ .min_keysize = CHACHA_KEY_SIZE,
+ .max_keysize = CHACHA_KEY_SIZE,
+ .ivsize = XCHACHA_IV_SIZE,
+ .chunksize = CHACHA_BLOCK_SIZE,
+ .walksize = 4 * CHACHA_BLOCK_SIZE,
+ .setkey = crypto_chacha12_setkey,
+ .encrypt = xchacha_neon,
+ .decrypt = xchacha_neon,
}
};

@@ -180,3 +197,5 @@ MODULE_ALIAS_CRYPTO("chacha20");
MODULE_ALIAS_CRYPTO("chacha20-neon");
MODULE_ALIAS_CRYPTO("xchacha20");
MODULE_ALIAS_CRYPTO("xchacha20-neon");
+MODULE_ALIAS_CRYPTO("xchacha12");
+MODULE_ALIAS_CRYPTO("xchacha12-neon");
--
2.19.1.1215.g8438c0b245-goog