Add support for large messages

src/ed25519.h

@@ -30,6 +30,10 @@ int ED25519_DECLSPEC ed25519_verify(const unsigned char *signature, const unsign
 void ED25519_DECLSPEC ed25519_add_scalar(unsigned char *public_key, unsigned char *private_key, const unsigned char *scalar);
 void ED25519_DECLSPEC ed25519_key_exchange(unsigned char *shared_secret, const unsigned char *public_key, const unsigned char *private_key);
 
+void * ED25519_DECLSPEC ed25519_verify_begin(const unsigned char *signature, const unsigned char *public_key);
+void ED25519_DECLSPEC ed25519_verify_update(void * hash, const unsigned char *message, size_t message_len);
+int ED25519_DECLSPEC ed25519_verify_end(void * hash, const unsigned char *signature);
+
 
 #ifdef __cplusplus
 }

src/verify.c

@@ -1,3 +1,6 @@
+#include <malloc.h>
+#include <string.h>
+
 #include "ed25519.h"
 #include "sha512.h"
 #include "ge.h"
@@ -64,7 +67,7 @@ int ed25519_verify(const unsigned char *signature, const unsigned char *message,
     sha512_update(&hash, public_key, 32);
     sha512_update(&hash, message, message_len);
     sha512_final(&hash, h);
-    
+
     sc_reduce(h);
     ge_double_scalarmult_vartime(&R, h, &A, signature + 32);
     ge_tobytes(checker, &R);
@@ -75,3 +78,55 @@ int ed25519_verify(const unsigned char *signature, const unsigned char *message,
 
     return 1;
 }
+
+typedef struct context_
+{
+   sha512_context hash;
+   ge_p3 A;
+} context;
+
+void * ed25519_verify_begin(const unsigned char *signature, const unsigned char *public_key) {
+    ge_p3 A;
+
+    if (signature[63] & 224) {
+        return NULL;
+    }
+
+    if (ge_frombytes_negate_vartime(&A, public_key) != 0) {
+        return NULL;
+    }
+
+    context * ctx = (context*) malloc(sizeof(context));
+
+    memcpy(&ctx->A, &A, sizeof(A));
+
+    sha512_init(&ctx->hash);
+    sha512_update(&ctx->hash, signature, 32);
+    sha512_update(&ctx->hash, public_key, 32);
+
+    return ctx;
+}
+
+void ed25519_verify_update(void * ctx, const unsigned char *message, size_t message_len) {
+    sha512_update(&((context*)ctx)->hash, message, message_len);
+}
+
+int ed25519_verify_end(void * ctx, const unsigned char *signature) {
+    unsigned char h[64];
+    unsigned char checker[32];
+    ge_p2 R;
+
+    sha512_final(&((context*)ctx)->hash, h);
+
+    sc_reduce(h);
+    ge_double_scalarmult_vartime(&R, h, &((context*)ctx)->A, signature + 32);
+    ge_tobytes(checker, &R);
+
+    free(ctx);
+
+    if (!consttime_equal(checker, signature)) {
+        return 0;
+    }
+
+    return 1;
+}