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Subject[RFC PATCH v2 07/12] crypto: arm/chacha - add XChaCha12 support
Date
From: Eric Biggers <ebiggers@google.com>

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.

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 0aa1471f27d2e..cc932d9bba561 100644
--- a/arch/arm/crypto/Kconfig
+++ b/arch/arm/crypto/Kconfig
@@ -117,7 +117,7 @@ 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 b236af4889c61..0b1b238227707 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>
*
@@ -160,6 +161,22 @@ 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,
}
};

@@ -186,3 +203,5 @@ 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");
--
2.19.1.331.ge82ca0e54c-goog
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