Support for compressed public key format

eth/keys/libsecp256k1.nim

@@ -12,6 +12,7 @@ import secp256k1, nimcrypto/sysrand, nimcrypto/utils
 
 const
   KeyLength* = 256 div 8
+  CompressedPubKeyLength* = 33
   RawSignatureSize* = KeyLength * 2 + 1
   RawPublicKeySize* = KeyLength * 2
   InvalidPrivateKey = "Invalid private key!"
@@ -154,9 +155,7 @@ proc recoverPublicKey*(data: openarray[byte],
   ## Unserialize public key from `data`.
   let ctx = getSecpContext()
   let length = len(data)
-  if length < RawPublicKeySize:
+  if length >= RawPublicKeySize:
-    setErrorMsg(InvalidPublicKey)
-    return(EthKeysStatus.Error)
     var rawkey: array[RawPublicKeySize + 1, byte]
     rawkey[0] = 0x04'u8 # mark key with UNCOMPRESSED flag
     copyMem(addr rawkey[1], unsafeAddr data[0], RawPublicKeySize)
@@ -164,6 +163,16 @@ proc recoverPublicKey*(data: openarray[byte],
                                 cast[ptr cuchar](addr rawkey),
                                 RawPublicKeySize + 1) != 1:
       return(EthKeysStatus.Error)
+  elif length == CompressedPubKeyLength:
+    # Compressed format
+    if secp256k1_ec_pubkey_parse(ctx, addr pubkey,
+                                cast[ptr cuchar](unsafeAddr data),
+                                length) != 1:
+      return(EthKeysStatus.Error)
+  else:
+    setErrorMsg(InvalidPublicKey)
+    return(EthKeysStatus.Error)
+
   result = EthKeysStatus.Success
 
 proc recoverSignature*(data: openarray[byte],
@@ -184,8 +193,6 @@ proc recoverSignature*(data: openarray[byte],
 proc initPublicKey*(hexstr: string): PublicKey =
   ## Create new public key from hexadecimal string representation.
   var o = fromHex(stripSpaces(hexstr))
-  if len(o) < RawPublicKeySize:
-    raise newException(EthKeysException, InvalidPublicKey)
   if recoverPublicKey(o, result) != EthKeysStatus.Success:
     raise newException(EthKeysException, InvalidPublicKey)
 
@@ -217,21 +224,17 @@ proc ecdhAgree*(seckey: PrivateKey, pubkey: PublicKey,
   copyMem(addr secret, addr res[1], KeyLength)
   return(EthKeysStatus.Success)
 
-proc getRaw*(pubkey: PublicKey): array[RawPublicKeySize, byte] {.noinit.} =
+proc toRaw*(pubkey: PublicKey, data: var openarray[byte], compressed = false) =
-  ## Converts public key `pubkey` to serialized form.
-  var key: array[RawPublicKeySize + 1, byte]
-  var length = csize(sizeof(key))
-  let ctx = getSecpContext()
-  if secp256k1_ec_pubkey_serialize(ctx, cast[ptr cuchar](addr key),
-                                   addr length, unsafeAddr pubkey,
-                                   SECP256K1_EC_UNCOMPRESSED) != 1:
-    raiseSecp256k1Error()
-  doAssert(length == RawPublicKeySize + 1)
-  doAssert(key[0] == 0x04'u8)
-  copyMem(addr result[0], addr key[1], RawPublicKeySize)
-
-proc toRaw*(pubkey: PublicKey, data: var openarray[byte]) =
   ## Converts public key `pubkey` to serialized form and store it in `data`.
+  if compressed:
+    var length = len(data)
+    doAssert(length >= CompressedPubKeyLength)
+    let ctx = getSecpContext()
+    if secp256k1_ec_pubkey_serialize(ctx, cast[ptr cuchar](addr data[0]),
+                                    addr length, unsafeAddr pubkey,
+                                    SECP256K1_EC_COMPRESSED) != 1:
+      raiseSecp256k1Error()
+  else:
     var key: array[RawPublicKeySize + 1, byte]
     doAssert(len(data) >= RawPublicKeySize)
     var length = csize(sizeof(key))
@@ -244,6 +247,14 @@ proc toRaw*(pubkey: PublicKey, data: var openarray[byte]) =
     doAssert(key[0] == 0x04'u8)
     copyMem(addr data[0], addr key[1], RawPublicKeySize)
 
+proc getRaw*(pubkey: PublicKey): array[RawPublicKeySize, byte] {.noinit, inline.} =
+  ## Converts public key `pubkey` to serialized form.
+  pubkey.toRaw(result)
+
+proc getRawCompressed*(pubkey: PublicKey): array[CompressedPubKeyLength, byte] {.noinit, inline.} =
+  ## Converts public key `pubkey` to serialized form.
+  pubkey.toRaw(result, true)
+
 proc getRaw*(s: Signature): array[RawSignatureSize, byte] {.noinit.} =
   ## Converts signature `s` to serialized form.
   let ctx = getSecpContext()

tests/keys/test_keys.nim

@@ -266,3 +266,12 @@ suite "ECC/ECDSA/ECDHE tests suite":
       pubkey1.isZeroKey() == true
       seckey2.isZeroKey() == false
       pubkey2.isZeroKey() == false
+
+  test "Compressed public keys":
+    let pubkeyCompressed = "03CA634CAE0D49ACB401D8A4C6B6FE8C55B70D115BF400769CC1400F3258CD3138"
+    let s = initPublicKey(pubkeyCompressed)
+    check:
+      s.getRaw.toHex == """CA634CAE0D49ACB401D8A4C6B6FE8C55B70D115BF400769CC1400F3258
+          CD31387574077F301B421BC84DF7266C44E9E6D569FC56BE00812904767BF5CCD1FC7F""".stripSpaces
+
+      s.getRawCompressed.toHex == pubkeyCompressed