Refactor/split ED25519_keypair.

This brings in ED25519_keypair_from_seed() from BoringSSL commit
c034e2d3ce16, which ED25519_keypair then wraps. This reduces differences
between us and BoringSSL.

2 files changed, 24 insertions, 16 deletions

diff --git a/src/lib/libcrypto/curve25519/curve25519.c b/src/lib/libcrypto/curve25519/curve25519.c
index 7713b8716c..8d29379eb2 100644
--- a/src/lib/libcrypto/curve25519/curve25519.c
+++ b/src/lib/libcrypto/curve25519/curve25519.c
@@ -1,4 +1,4 @@
-/*      $OpenBSD: curve25519.c,v 1.9 2022/11/08 17:01:57 jsing Exp $ */
+/*      $OpenBSD: curve25519.c,v 1.10 2022/11/08 17:07:17 jsing Exp $ */
 /*
  * Copyright (c) 2015, Google Inc.
  *
@@ -4618,20 +4618,7 @@ sc_muladd(uint8_t *s, const uint8_t *a, const uint8_t *b,
 void ED25519_keypair(uint8_t out_public_key[32], uint8_t out_private_key[64]) {
   uint8_t seed[32];
   arc4random_buf(seed, 32);
-
-  uint8_t az[SHA512_DIGEST_LENGTH];
-  SHA512(seed, 32, az);
-
-  az[0] &= 248;
-  az[31] &= 63;
-  az[31] |= 64;
-
-  ge_p3 A;
-  x25519_ge_scalarmult_base(&A, az);
-  ge_p3_tobytes(out_public_key, &A);
-
-  memcpy(out_private_key, seed, 32);
-  memmove(out_private_key + 32, out_public_key, 32);
+  ED25519_keypair_from_seed(out_public_key, out_private_key, seed);
 }
 
 int ED25519_sign(uint8_t *out_sig, const uint8_t *message, size_t message_len,
@@ -4705,6 +4692,24 @@ int ED25519_verify(const uint8_t *message, size_t message_len,
   return timingsafe_memcmp(rcheck, rcopy, sizeof(rcheck)) == 0;
 }
 
+void ED25519_keypair_from_seed(uint8_t out_public_key[32],
+                               uint8_t out_private_key[64],
+                               const uint8_t seed[32]) {
+  uint8_t az[SHA512_DIGEST_LENGTH];
+  SHA512(seed, 32, az);
+
+  az[0] &= 248;
+  az[31] &= 63;
+  az[31] |= 64;
+
+  ge_p3 A;
+  x25519_ge_scalarmult_base(&A, az);
+  ge_p3_tobytes(out_public_key, &A);
+
+  memcpy(out_private_key, seed, 32);
+  memcpy(out_private_key + 32, out_public_key, 32);
+}
+
 /* Replace (f,g) with (g,f) if b == 1;
  * replace (f,g) with (f,g) if b == 0.
  *
diff --git a/src/lib/libcrypto/curve25519/curve25519_internal.h b/src/lib/libcrypto/curve25519/curve25519_internal.h
index 09d20a4fec..9d2ee9b4d7 100644
--- a/src/lib/libcrypto/curve25519/curve25519_internal.h
+++ b/src/lib/libcrypto/curve25519/curve25519_internal.h
@@ -1,4 +1,4 @@
-/*      $OpenBSD: curve25519_internal.h,v 1.3 2019/05/11 15:55:52 tb Exp $ */
+/*      $OpenBSD: curve25519_internal.h,v 1.4 2022/11/08 17:07:17 jsing Exp $ */
 /*
  * Copyright (c) 2015, Google Inc.
  *
@@ -94,6 +94,9 @@ void x25519_scalar_mult(uint8_t out[32], const uint8_t scalar[32],
 void x25519_scalar_mult_generic(uint8_t out[32], const uint8_t scalar[32],
     const uint8_t point[32]);
 
+void ED25519_keypair_from_seed(uint8_t out_public_key[32],
+    uint8_t out_private_key[64], const uint8_t seed[32]);
+
 __END_HIDDEN_DECLS
 
 #endif  /* HEADER_CURVE25519_INTERNAL_H */