Fix leading zero bytes in DSA, ECDSA, ECGDSA and ECKCDSA signatures

6 files changed, 26 insertions, 16 deletions

diff --git a/src/lib/math/bigint/big_code.cpp b/src/lib/math/bigint/big_code.cpp
index 299fdc246..c8687715d 100644
--- a/src/lib/math/bigint/big_code.cpp
+++ b/src/lib/math/bigint/big_code.cpp
@@ -98,6 +98,17 @@ void BigInt::encode_1363(byte output[], size_t bytes, const BigInt& n)
    }
 
 /*
+* Encode two BigInt, with leading 0s if needed, and concatenate
+*/
+secure_vector<byte> BigInt::encode_fixed_length_int_pair(const BigInt& n1, const BigInt& n2, size_t bytes)
+   {
+   secure_vector<byte> output(2 * bytes);
+   BigInt::encode_1363(output.data(), bytes, n1);
+   BigInt::encode_1363(output.data() + bytes, bytes, n2);
+   return output;
+   }
+
+/*
 * Decode a BigInt
 */
 BigInt BigInt::decode(const byte buf[], size_t length, Base base)
diff --git a/src/lib/math/bigint/bigint.h b/src/lib/math/bigint/bigint.h
index 2963ba35d..a61bee39c 100644
--- a/src/lib/math/bigint/bigint.h
+++ b/src/lib/math/bigint/bigint.h
@@ -566,6 +566,15 @@ class BOTAN_DLL BigInt
 
      static void encode_1363(byte out[], size_t bytes, const BigInt& n);
 
+     /**
+     * Encode two BigInt to a byte array according to IEEE 1363
+     * @param n1 the first BigInt to encode
+     * @param n2 the second BigInt to encode
+     * @param bytes the length of the encoding of each single BigInt
+     * @result a secure_vector<byte> containing the concatenation of the two encoded BigInt
+     */
+     static secure_vector<byte> encode_fixed_length_int_pair(const BigInt& n1, const BigInt& n2, size_t bytes);
+
    private:
       secure_vector<word> m_reg;
       Sign m_signedness = Positive;
diff --git a/src/lib/pubkey/dsa/dsa.cpp b/src/lib/pubkey/dsa/dsa.cpp
index 6effb81dd..399756b1a 100644
--- a/src/lib/pubkey/dsa/dsa.cpp
+++ b/src/lib/pubkey/dsa/dsa.cpp
@@ -133,10 +133,7 @@ DSA_Signature_Operation::raw_sign(const byte msg[], size_t msg_len,
    BOTAN_ASSERT(s != 0, "invalid s");
    BOTAN_ASSERT(r != 0, "invalid r");
 
-   secure_vector<byte> output(2*m_q.bytes());
-   r.binary_encode(&output[output.size() / 2 - r.bytes()]);
-   s.binary_encode(&output[output.size() - s.bytes()]);
-   return output;
+   return BigInt::encode_fixed_length_int_pair(r, s, m_q.bytes());
    }
 
 /**
diff --git a/src/lib/pubkey/ecdsa/ecdsa.cpp b/src/lib/pubkey/ecdsa/ecdsa.cpp
index 6fe7ce319..264a36963 100644
--- a/src/lib/pubkey/ecdsa/ecdsa.cpp
+++ b/src/lib/pubkey/ecdsa/ecdsa.cpp
@@ -86,10 +86,7 @@ ECDSA_Signature_Operation::raw_sign(const byte msg[], size_t msg_len,
    BOTAN_ASSERT(s != 0, "invalid s");
    BOTAN_ASSERT(r != 0, "invalid r");
 
-   secure_vector<byte> output(2*m_order.bytes());
-   r.binary_encode(&output[output.size() / 2 - r.bytes()]);
-   s.binary_encode(&output[output.size() - s.bytes()]);
-   return output;
+   return BigInt::encode_fixed_length_int_pair(r, s, m_order.bytes());
    }
 
 /**
diff --git a/src/lib/pubkey/ecgdsa/ecgdsa.cpp b/src/lib/pubkey/ecgdsa/ecgdsa.cpp
index 3e14aa8f4..30ea32817 100644
--- a/src/lib/pubkey/ecgdsa/ecgdsa.cpp
+++ b/src/lib/pubkey/ecgdsa/ecgdsa.cpp
@@ -73,10 +73,7 @@ ECGDSA_Signature_Operation::raw_sign(const byte msg[], size_t msg_len,
    BOTAN_ASSERT(s != 0, "invalid s");
    BOTAN_ASSERT(r != 0, "invalid r");
 
-   secure_vector<byte> output(2*m_order.bytes());
-   r.binary_encode(&output[output.size() / 2 - r.bytes()]);
-   s.binary_encode(&output[output.size() - s.bytes()]);
-   return output;
+   return BigInt::encode_fixed_length_int_pair(r, s, m_order.bytes());
    }
 
 /**
diff --git a/src/lib/pubkey/eckcdsa/eckcdsa.cpp b/src/lib/pubkey/eckcdsa/eckcdsa.cpp
index 83439332e..5ca89675c 100644
--- a/src/lib/pubkey/eckcdsa/eckcdsa.cpp
+++ b/src/lib/pubkey/eckcdsa/eckcdsa.cpp
@@ -100,10 +100,9 @@ ECKCDSA_Signature_Operation::raw_sign(const byte msg[], size_t,
    const BigInt s = m_mod_order.multiply(m_x, k - w);
    BOTAN_ASSERT(s != 0, "invalid s");
 
-   secure_vector<byte> signature(r.bytes() + s.bytes());
-   r.binary_encode(signature.data());
-   s.binary_encode(&signature[r.bytes()]);
-   return signature;
+   secure_vector<byte> output = BigInt::encode_1363(r, c.size());
+   output += BigInt::encode_1363(s, m_mod_order.get_modulus().bytes());
+   return output;
    }
 
 /**