crypto: poly1305 - add Poly1305 core API

Expose a low-level Poly1305 API which implements the
ε-almost-∆-universal (εA∆U) hash function underlying the Poly1305 MAC
and supports block-aligned inputs only.

This is needed for Adiantum hashing, which builds an εA∆U hash function
from NH and a polynomial evaluation in GF(2^{130}-5); this polynomial
evaluation is identical to the one the Poly1305 MAC does.  However, the
crypto_shash Poly1305 API isn't very appropriate for this because its
calling convention assumes it is used as a MAC, with a 32-byte "one-time
key" provided for every digest.

But by design, in Adiantum hashing the performance of the polynomial
evaluation isn't nearly as critical as NH.  So it suffices to just have
some C helper functions.  Thus, this patch adds such functions.

Acked-by: Martin Willi <martin@strongswan.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

1 files changed, 16 insertions, 0 deletions

diff --git a/include/crypto/poly1305.h b/include/crypto/poly1305.h
index 493244c46664..34317ed2071e 100644
--- a/include/crypto/poly1305.h
+++ b/include/crypto/poly1305.h
@@ -38,6 +38,22 @@ struct poly1305_desc_ctx {
 	bool sset;
 };
 
+/*
+ * Poly1305 core functions.  These implement the ε-almost-∆-universal hash
+ * function underlying the Poly1305 MAC, i.e. they don't add an encrypted nonce
+ * ("s key") at the end.  They also only support block-aligned inputs.
+ */
+void poly1305_core_setkey(struct poly1305_key *key, const u8 *raw_key);
+static inline void poly1305_core_init(struct poly1305_state *state)
+{
+	memset(state->h, 0, sizeof(state->h));
+}
+void poly1305_core_blocks(struct poly1305_state *state,
+			  const struct poly1305_key *key,
+			  const void *src, unsigned int nblocks);
+void poly1305_core_emit(const struct poly1305_state *state, void *dst);
+
+/* Crypto API helper functions for the Poly1305 MAC */
 int crypto_poly1305_init(struct shash_desc *desc);
 unsigned int crypto_poly1305_setdesckey(struct poly1305_desc_ctx *dctx,
 					const u8 *src, unsigned int srclen);