From: Daiki Ueno dueno@redhat.com
The ChaCha-Poly1305 implementation previously used the chacha_crypt function that assumes the block counter is 64-bit long, while RFC 8439 defines that the counter is 32-bit long. Although this should be fine as long as up to 256 gigabytes of data is encrypted with the same key, it would be nice to use a separate functions (chacha_set_counter32 and chacha_crypt32) that assume the counter is 32-bit long.
Signed-off-by: Daiki Ueno dueno@redhat.com --- chacha-crypt.c | 32 ++++++++++++++++++++++++++++++++ chacha-poly1305.c | 4 ++-- chacha-set-nonce.c | 6 ++++++ chacha.h | 10 ++++++++++ nettle.texinfo | 31 +++++++++++++++++++++++++++++++ testsuite/chacha-test.c | 34 ++++++++++++++++++++++++++++++---- 6 files changed, 111 insertions(+), 6 deletions(-)
diff --git a/chacha-crypt.c b/chacha-crypt.c index 63d799ce..0bb44ed9 100644 --- a/chacha-crypt.c +++ b/chacha-crypt.c @@ -85,3 +85,35 @@ chacha_crypt(struct chacha_ctx *ctx, m += CHACHA_BLOCK_SIZE; } } + +void +chacha_crypt32(struct chacha_ctx *ctx, + size_t length, + uint8_t *c, + const uint8_t *m) +{ + if (!length) + return; + + for (;;) + { + uint32_t x[_CHACHA_STATE_LENGTH]; + + _chacha_core (x, ctx->state, CHACHA_ROUNDS); + + ++ctx->state[12]; + + /* stopping at 2^70 length per nonce is user's responsibility */ + + if (length <= CHACHA_BLOCK_SIZE) + { + memxor3 (c, m, x, length); + return; + } + memxor3 (c, m, x, CHACHA_BLOCK_SIZE); + + length -= CHACHA_BLOCK_SIZE; + c += CHACHA_BLOCK_SIZE; + m += CHACHA_BLOCK_SIZE; + } +} diff --git a/chacha-poly1305.c b/chacha-poly1305.c index 974a5022..a15fef0c 100644 --- a/chacha-poly1305.c +++ b/chacha-poly1305.c @@ -130,7 +130,7 @@ chacha_poly1305_encrypt (struct chacha_poly1305_ctx *ctx, assert (ctx->data_size % CHACHA_POLY1305_BLOCK_SIZE == 0); poly1305_pad (ctx);
- chacha_crypt (&ctx->chacha, length, dst, src); + chacha_crypt32 (&ctx->chacha, length, dst, src); poly1305_update (ctx, length, dst); ctx->data_size += length; } @@ -146,7 +146,7 @@ chacha_poly1305_decrypt (struct chacha_poly1305_ctx *ctx, poly1305_pad (ctx);
poly1305_update (ctx, length, src); - chacha_crypt (&ctx->chacha, length, dst, src); + chacha_crypt32 (&ctx->chacha, length, dst, src); ctx->data_size += length; } diff --git a/chacha-set-nonce.c b/chacha-set-nonce.c index 2c34e498..1547aea1 100644 --- a/chacha-set-nonce.c +++ b/chacha-set-nonce.c @@ -75,3 +75,9 @@ chacha_set_counter(struct chacha_ctx *ctx, const uint8_t *counter) ctx->state[12] = LE_READ_UINT32(counter + 0); ctx->state[13] = LE_READ_UINT32(counter + 4); } + +void +chacha_set_counter32(struct chacha_ctx *ctx, const uint8_t *counter) +{ + ctx->state[12] = LE_READ_UINT32(counter + 0); +} diff --git a/chacha.h b/chacha.h index 440fe968..fe28b835 100644 --- a/chacha.h +++ b/chacha.h @@ -47,7 +47,9 @@ extern "C" { #define chacha_set_nonce nettle_chacha_set_nonce #define chacha_set_nonce96 nettle_chacha_set_nonce96 #define chacha_set_counter nettle_chacha_set_counter +#define chacha_set_counter32 nettle_chacha_set_counter32 #define chacha_crypt nettle_chacha_crypt +#define chacha_crypt32 nettle_chacha_crypt32
/* Currently, only 256-bit keys are supported. */ #define CHACHA_KEY_SIZE 32 @@ -55,6 +57,7 @@ extern "C" { #define CHACHA_NONCE_SIZE 8 #define CHACHA_NONCE96_SIZE 12 #define CHACHA_COUNTER_SIZE 8 +#define CHACHA_COUNTER32_SIZE 4
#define _CHACHA_STATE_LENGTH 16
@@ -86,10 +89,17 @@ chacha_set_nonce96(struct chacha_ctx *ctx, const uint8_t *nonce); void chacha_set_counter(struct chacha_ctx *ctx, const uint8_t *counter);
+void +chacha_set_counter32(struct chacha_ctx *ctx, const uint8_t *counter); + void chacha_crypt(struct chacha_ctx *ctx, size_t length, uint8_t *dst, const uint8_t *src);
+void +chacha_crypt32(struct chacha_ctx *ctx, size_t length, + uint8_t *dst, const uint8_t *src); + #ifdef __cplusplus } #endif diff --git a/nettle.texinfo b/nettle.texinfo index 0b339f51..fe44f6af 100644 --- a/nettle.texinfo +++ b/nettle.texinfo @@ -1700,6 +1700,37 @@ all but the last call @emph{must} use a length that is a multiple of @code{CHACHA_BLOCK_SIZE}. @end deftypefun
+@subsubsection 32-bit counter variant + +While the original paper uses 64-bit counter value, the variant defined +in @cite{RFC 8439} uses 32-bit counter value. This variant is +particularly useful for @pxref{ChaCha-Poly1305} AEAD construction, which +supports 12-octet nonces. + +@defvr Constant CHACHA_NONCE96_SIZE +Size of the nonce, 12. +@end defvr + +@defvr Constant CHACHA_COUNTER32_SIZE +Size of the counter, 4. +@end defvr + +@deftypefun void chacha_set_nonce96 (struct chacha_ctx *@var{ctx}, const uint8_t *@var{nonce}) +Sets the nonce. This is similar to the above @code{chacha_set_nonce}, +but the input is always of size @code{CHACHA_NONCE96_SIZE}, 12 octets. +@end deftypefun + +@deftypefun void chacha_set_counter32 (struct chacha_ctx *@var{ctx}, const uint8_t *@var{counter}) +Sets the block counter. This is similar to the above @code{chacha_set_counter}, +but the input is always of size @code{CHACHA_COUNTER32_SIZE}, 4 octets. +@end deftypefun + +@deftypefun void chacha_crypt32 (struct chacha_ctx *@var{ctx}, size_t @var{length}, uint8_t *@var{dst}, const uint8_t *@var{src}) +Encrypts or decrypts the data of a message, using ChaCha. This is similar to the +above @code{chacha_crypt}, but it assumes the internal counter value is 32-bit +long and the nonce is 96-bit long. +@end deftypefun + @subsection DES @cindex DES DES is the old Data Encryption Standard, specified by NIST. It uses a diff --git a/testsuite/chacha-test.c b/testsuite/chacha-test.c index 6875d4bb..fb8f1db7 100644 --- a/testsuite/chacha-test.c +++ b/testsuite/chacha-test.c @@ -71,9 +71,23 @@ _test_chacha(const struct tstring *key, const struct tstring *nonce, die ("Bad nonce size %u.\n", (unsigned) nonce->length);
if (counter) - chacha_set_counter(&ctx, counter->data); + { + if (counter->length == CHACHA_COUNTER_SIZE) + { + ASSERT (nonce->length == CHACHA_NONCE_SIZE); + chacha_set_counter(&ctx, counter->data); + } + else if (counter->length == CHACHA_COUNTER32_SIZE) + { + ASSERT (nonce->length == CHACHA_NONCE96_SIZE); + chacha_set_counter32(&ctx, counter->data); + } + }
- chacha_crypt (&ctx, length, data, data); + if (nonce->length == CHACHA_NONCE_SIZE) + chacha_crypt (&ctx, length, data, data); + else + chacha_crypt32 (&ctx, length, data, data);
ASSERT (data[-1] == 17); ASSERT (data[length] == 17); @@ -666,8 +680,20 @@ test_main(void) "b5129cd1de164eb9 cbd083e8a2503c4e"), 20);
- /* This is identical to the 96-bit nonce test, but it manually sets - the counter value */ + /* This is identical to the above 96-bit nonce test, but it manually + sets the 32-bit counter value */ + test_chacha_with_counter(SHEX("0001020304050607 08090a0b0c0d0e0f" + "1011121314151617 18191a1b1c1d1e1f"), + SHEX("000000090000004a 00000000"), + SHEX("10f1e7e4d13b5915 500fdd1fa32071c4" + "c7d1f4c733c06803 0422aa9ac3d46c4e" + "d2826446079faa09 14c2d705d98b02a2" + "b5129cd1de164eb9 cbd083e8a2503c4e"), + 20, + SHEX("01000000")); + + /* This is identical to the above 96-bit nonce test, but it manually + sets the 64-bit counter value */ test_chacha_with_counter(SHEX("0001020304050607 08090a0b0c0d0e0f" "1011121314151617 18191a1b1c1d1e1f"), SHEX("0000004a00000000"),