From bbe67d8b29f31b140d6987d82912f48539c8bcb7 Mon Sep 17 00:00:00 2001
From: Pieter Wuille <pieter.wuille@gmail.com>
Date: Tue, 18 Nov 2014 12:32:53 +0100
Subject: [PATCH] Make secp256k1_eckey_pubkey_serialize fail for infinity

---
 src/eckey.h      |  2 +-
 src/eckey_impl.h | 16 +++++++++++++---
 src/secp256k1.c  | 13 +++++--------
 3 files changed, 19 insertions(+), 12 deletions(-)

diff --git a/src/eckey.h b/src/eckey.h
index 725a5494d6..024c8b821b 100644
--- a/src/eckey.h
+++ b/src/eckey.h
@@ -12,7 +12,7 @@
 #include "num.h"
 
 static int secp256k1_eckey_pubkey_parse(secp256k1_ge_t *elem, const unsigned char *pub, int size);
-static void secp256k1_eckey_pubkey_serialize(secp256k1_ge_t *elem, unsigned char *pub, int *size, int compressed);
+static int secp256k1_eckey_pubkey_serialize(secp256k1_ge_t *elem, unsigned char *pub, int *size, int compressed);
 
 static int secp256k1_eckey_privkey_parse(secp256k1_scalar_t *key, const unsigned char *privkey, int privkeylen);
 static int secp256k1_eckey_privkey_serialize(unsigned char *privkey, int *privkeylen, const secp256k1_scalar_t *key, int compressed);
diff --git a/src/eckey_impl.h b/src/eckey_impl.h
index 59b191d1bd..290b1f0900 100644
--- a/src/eckey_impl.h
+++ b/src/eckey_impl.h
@@ -32,7 +32,10 @@ static int secp256k1_eckey_pubkey_parse(secp256k1_ge_t *elem, const unsigned cha
     }
 }
 
-static void secp256k1_eckey_pubkey_serialize(secp256k1_ge_t *elem, unsigned char *pub, int *size, int compressed) {
+static int secp256k1_eckey_pubkey_serialize(secp256k1_ge_t *elem, unsigned char *pub, int *size, int compressed) {
+    if (secp256k1_ge_is_infinity(elem)) {
+        return 0;
+    }
     secp256k1_fe_normalize(&elem->x);
     secp256k1_fe_normalize(&elem->y);
     secp256k1_fe_get_b32(&pub[1], &elem->x);
@@ -44,6 +47,7 @@ static void secp256k1_eckey_pubkey_serialize(secp256k1_ge_t *elem, unsigned char
         pub[0] = 0x04;
         secp256k1_fe_get_b32(&pub[33], &elem->y);
     }
+    return 1;
 }
 
 static int secp256k1_eckey_privkey_parse(secp256k1_scalar_t *key, const unsigned char *privkey, int privkeylen) {
@@ -107,7 +111,10 @@ static int secp256k1_eckey_privkey_serialize(unsigned char *privkey, int *privke
         secp256k1_scalar_get_b32(ptr, key); ptr += 32;
         memcpy(ptr, middle, sizeof(middle)); ptr += sizeof(middle);
         int pubkeylen = 0;
-        secp256k1_eckey_pubkey_serialize(&r, ptr, &pubkeylen, 1); ptr += pubkeylen;
+        if (!secp256k1_eckey_pubkey_serialize(&r, ptr, &pubkeylen, 1)) {
+            return 0;
+        }
+        ptr += pubkeylen;
         *privkeylen = ptr - privkey;
     } else {
         static const unsigned char begin[] = {
@@ -131,7 +138,10 @@ static int secp256k1_eckey_privkey_serialize(unsigned char *privkey, int *privke
         secp256k1_scalar_get_b32(ptr, key); ptr += 32;
         memcpy(ptr, middle, sizeof(middle)); ptr += sizeof(middle);
         int pubkeylen = 0;
-        secp256k1_eckey_pubkey_serialize(&r, ptr, &pubkeylen, 0); ptr += pubkeylen;
+        if (!secp256k1_eckey_pubkey_serialize(&r, ptr, &pubkeylen, 0)) {
+            return 0;
+        }
+        ptr += pubkeylen;
         *privkeylen = ptr - privkey;
     }
     return 1;
diff --git a/src/secp256k1.c b/src/secp256k1.c
index a7d9d16c62..1ab5b3722c 100644
--- a/src/secp256k1.c
+++ b/src/secp256k1.c
@@ -150,8 +150,7 @@ int secp256k1_ecdsa_recover_compact(const unsigned char *msg, int msglen, const
 
     secp256k1_ge_t q;
     if (secp256k1_ecdsa_sig_recover(&sig, &q, &m, recid)) {
-        secp256k1_eckey_pubkey_serialize(&q, pubkey, pubkeylen, compressed);
-        ret = 1;
+        ret = secp256k1_eckey_pubkey_serialize(&q, pubkey, pubkeylen, compressed);
     }
     return ret;
 }
@@ -187,8 +186,7 @@ int secp256k1_ec_pubkey_create(unsigned char *pubkey, int *pubkeylen, const unsi
     secp256k1_scalar_clear(&sec);
     secp256k1_ge_t p;
     secp256k1_ge_set_gej(&p, &pj);
-    secp256k1_eckey_pubkey_serialize(&p, pubkey, pubkeylen, compressed);
-    return 1;
+    return secp256k1_eckey_pubkey_serialize(&p, pubkey, pubkeylen, compressed);
 }
 
 int secp256k1_ec_pubkey_decompress(unsigned char *pubkey, int *pubkeylen) {
@@ -198,8 +196,7 @@ int secp256k1_ec_pubkey_decompress(unsigned char *pubkey, int *pubkeylen) {
     secp256k1_ge_t p;
     if (!secp256k1_eckey_pubkey_parse(&p, pubkey, *pubkeylen))
         return 0;
-    secp256k1_eckey_pubkey_serialize(&p, pubkey, pubkeylen, 0);
-    return 1;
+    return secp256k1_eckey_pubkey_serialize(&p, pubkey, pubkeylen, 0);
 }
 
 int secp256k1_ec_privkey_tweak_add(unsigned char *seckey, const unsigned char *tweak) {
@@ -236,7 +233,7 @@ int secp256k1_ec_pubkey_tweak_add(unsigned char *pubkey, int pubkeylen, const un
     }
     if (ret) {
         int oldlen = pubkeylen;
-        secp256k1_eckey_pubkey_serialize(&p, pubkey, &pubkeylen, oldlen <= 33);
+        ret = secp256k1_eckey_pubkey_serialize(&p, pubkey, &pubkeylen, oldlen <= 33);
         VERIFY_CHECK(pubkeylen == oldlen);
     }
 
@@ -276,7 +273,7 @@ int secp256k1_ec_pubkey_tweak_mul(unsigned char *pubkey, int pubkeylen, const un
     }
     if (ret) {
         int oldlen = pubkeylen;
-        secp256k1_eckey_pubkey_serialize(&p, pubkey, &pubkeylen, oldlen <= 33);
+        ret = secp256k1_eckey_pubkey_serialize(&p, pubkey, &pubkeylen, oldlen <= 33);
         VERIFY_CHECK(pubkeylen == oldlen);
     }