Eliminate max message size for signatures.

Dynamically allocate working buffers instead.

Closes #3

android/jni/ed25519/additions/curve_sigs.c

@@ -40,10 +40,10 @@ int curve25519_sign(unsigned char* signature_out,
 {
   ge_p3 ed_pubkey_point; /* Ed25519 pubkey point */
   unsigned char ed_pubkey[32]; /* Ed25519 encoded pubkey */
-  unsigned char sigbuf[MAX_MSG_LEN + 128]; /* working buffer */
+  unsigned char *sigbuf; /* working buffer */
   unsigned char sign_bit = 0;
 
-  if (msg_len > MAX_MSG_LEN) {
+  if ((sigbuf = malloc(msg_len + 128)) == 0) {
     memset(signature_out, 0, 64);
     return -1;
   }
@@ -61,6 +61,8 @@ int curve25519_sign(unsigned char* signature_out,
   /* Encode the sign bit into signature (in unused high bit of S) */
    signature_out[63] &= 0x7F; /* bit should be zero already, but just in case */
    signature_out[63] |= sign_bit;
+
+   free(sigbuf);
    return 0;
 }
 
@@ -73,11 +75,18 @@ int curve25519_verify(const unsigned char* signature,
   fe ed_y;
   unsigned char ed_pubkey[32];
   unsigned long long some_retval;
-  unsigned char verifybuf[MAX_MSG_LEN + 64]; /* working buffer */
-  unsigned char verifybuf2[MAX_MSG_LEN + 64]; /* working buffer #2 */
+  unsigned char *verifybuf = NULL; /* working buffer */
+  unsigned char *verifybuf2 = NULL; /* working buffer #2 */
+  int result;
 
-  if (msg_len > MAX_MSG_LEN) {
-    return -1;
+  if ((verifybuf = malloc(msg_len + 64)) == 0) {
+    result = -1;
+    goto err;
+  }
+
+  if ((verifybuf2 = malloc(msg_len + 64)) == 0) {
+    result = -1;
+    goto err;
   }
 
   /* Convert the Curve25519 public key into an Ed25519 public key.  In
@@ -112,5 +121,17 @@ int curve25519_verify(const unsigned char* signature,
   /* verifybuf2 = internal to next call gets a copy of verifybuf, S gets 
      replaced with pubkey for hashing, then the whole thing gets zeroized
      (if bad sig), or contains a copy of msg (good sig) */
-  return crypto_sign_open(verifybuf2, &some_retval, verifybuf, 64 + msg_len, ed_pubkey);
+  result = crypto_sign_open(verifybuf2, &some_retval, verifybuf, 64 + msg_len, ed_pubkey);
+
+  err:
+
+  if (verifybuf != NULL) {
+    free(verifybuf);
+  }
+
+  if (verifybuf2 != NULL) {
+    free(verifybuf2);
+  }
+
+  return result;
 }

android/jni/ed25519/additions/curve_sigs.h

@@ -2,8 +2,6 @@
 #ifndef __CURVE_SIGS_H__
 #define __CURVE_SIGS_H__
 
-#define MAX_MSG_LEN 256
-
 void curve25519_keygen(unsigned char* curve25519_pubkey_out, /* 32 bytes */
                        const unsigned char* curve25519_privkey_in); /* 32 bytes */
 

common/src/main/java/org/whispersystems/curve25519/java/curve_sigs.java

@@ -2,8 +2,6 @@ package org.whispersystems.curve25519.java;
 
 public class curve_sigs {
 
-    public static int MAX_MSG_LEN = 256;
-
     public static void curve25519_keygen(byte[] curve25519_pubkey_out,
                            byte[] curve25519_privkey_in)
     {
@@ -39,19 +37,14 @@ public class curve_sigs {
 
     public static int curve25519_sign(Sha512 sha512provider, byte[] signature_out,
                         byte[] curve25519_privkey,
-                        byte[] msg, long msg_len,
+                        byte[] msg, int msg_len,
                         byte[] random)
     {
       ge_p3 ed_pubkey_point = new ge_p3(); /* Ed25519 pubkey point */
       byte[] ed_pubkey = new byte[32]; /* Ed25519 encoded pubkey */
-      byte[] sigbuf = new byte[MAX_MSG_LEN + 128]; /* working buffer */
+      byte[] sigbuf = new byte[msg_len + 128]; /* working buffer */
       byte sign_bit = 0;
 
-      if (msg_len > MAX_MSG_LEN) {
-        Arrays.fill(signature_out, (byte)0);
-        return -1;
-      }
-
       /* Convert the Curve25519 privkey to an Ed25519 public key */
       ge_scalarmult_base.ge_scalarmult_base(ed_pubkey_point, curve25519_privkey);
       ge_p3_tobytes.ge_p3_tobytes(ed_pubkey, ed_pubkey_point);
@@ -70,7 +63,7 @@ public class curve_sigs {
 
     public static int curve25519_verify(Sha512 sha512provider, byte[] signature,
                           byte[] curve25519_pubkey,
-                          byte[] msg, long msg_len)
+                          byte[] msg, int msg_len)
     {
       int[] mont_x = new int[10];
       int[] mont_x_minus_one = new int[10];
@@ -80,12 +73,8 @@ public class curve_sigs {
       int[] ed_y = new int[10];
       byte[] ed_pubkey = new byte[32];
       long some_retval = 0;
-      byte[] verifybuf = new byte[MAX_MSG_LEN + 64]; /* working buffer */
-      byte[] verifybuf2 = new byte[MAX_MSG_LEN + 64]; /* working buffer #2 */
-
-      if (msg_len > MAX_MSG_LEN) {
-        return -1;
-      }
+      byte[] verifybuf = new byte[msg_len + 64]; /* working buffer */
+      byte[] verifybuf2 = new byte[msg_len + 64]; /* working buffer #2 */
 
       /* Convert the Curve25519 public key into an Ed25519 public key.  In
          particular, convert Curve25519's "montgomery" x-coordinate into an

j2me/src/test/java/org/whispersystems/curve25519/FakeSecureRandomProvider.java

@@ -4,4 +4,8 @@ public class FakeSecureRandomProvider implements SecureRandomProvider {
   public void nextBytes(byte[] output) {
 
   }
+
+  public int nextInt(int maxValue) {
+    return maxValue;
+  }
 }

tests/src/main/java/org/whispersystems/curve25519/Curve25519Test.java

@@ -130,18 +130,16 @@ public abstract class Curve25519Test extends TestCase {
     }
   }
 
-  public void testSignatureOverflow() throws NoSuchAlgorithmException, InvalidKeyException, NoSuchProviderException {
-    Curve25519KeyPair keys         = getInstance().generateKeyPair();
-    byte[]            message      = new byte[4096];
+  public void testLargeSignatures() throws NoSuchAlgorithmException, InvalidKeyException, NoSuchProviderException {
+    Curve25519KeyPair keys      = getInstance().generateKeyPair();
+    byte[]            message   = new byte[1024 * 1024];
+    byte[]            signature = getInstance().calculateSignature(keys.getPrivateKey(), message);
 
-    try {
-      byte[] signature = getInstance().calculateSignature(keys.getPrivateKey(), message);
-      throw new InvalidKeyException("Should have asserted!");
-    } catch (AssertionError e) {
-      // Success!
-    } catch (IllegalArgumentException iae) {
-      // Success !
-    }
+    assertTrue(getInstance().verifySignature(keys.getPublicKey(), message, signature));
+
+    signature[0] ^= 0x01;
+
+    assertFalse(getInstance().verifySignature(keys.getPublicKey(), message, signature));
   }
 
   protected Curve25519 getInstance() throws NoSuchProviderException {