diff --git a/requirements.txt b/requirements.txt
index b017276..20516a6 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,2 +1,4 @@
 web3
-ipfsapi
\ No newline at end of file
+ipfsapi
+pysha3
+secp256k1
diff --git a/servicesExternal/web3_single.py b/servicesExternal/web3_single.py
index 63e18e6..069dd96 100644
--- a/servicesExternal/web3_single.py
+++ b/servicesExternal/web3_single.py
@@ -5,7 +5,8 @@
 
 from config import config
 from lib.etherum_abi_perso import toSolidityBytes32 as etherumToSolid
-
+import secp256k1
+import sha3
 
 class Singleton(type):
     _instances = {}
@@ -182,6 +183,50 @@ def areSameAddressesNoChecksum(self, address1: str, address2: str) -> bool:
             return False
         return address1.toLowerCase() == address2.toLowerCase()
 
+    def keccak(byteMessage: bytes) -> str:
+        return sha3.keccak_256(byteMessage).digest()
+
+    def messageHash(message: bytes) -> str:
+	'''
+	Returns the keccak-256 hash of message, prefixed with the header used by the eth_sign RPC call
+	ethereumjs-util equivalent: https://github.com/ethereumjs/ethereumjs-util/blob/master/docs/index.md#hashpersonalmessage
+	'''
+        if not isinstance(message, bytes):
+	    message = message.encode('utf8')
+        prefix = '\u0019Ethereum Signed Message:\n' + str(len(message))
+        prefix = prefix.encode('utf8')
+        return keccak(prefix + message)
+
+    def legendreCheck(r: int) -> bool:
+        # Legendre symbol check; the secp256k1 library does not seem to do this
+        SECP256K1P = 2**256 - 4294968273
+        xc = r * r * r + 7
+        return pow(xc, (SECP256K1P - 1) // 2, SECP256K1P) == 1
+
+    def ecrecoverToPub(hash: str, signature: str, chaincode: int = 27) -> str:
+	'''
+	ECDSA public key recovery from signature
+	ethereumjs-util equivalent: https://github.com/ethereumjs/ethereumjs-util/blob/master/docs/index.md#ecrecover
+	'''
+        assert len(hash) == 32 # Keccak-256 in Solidity returns a bytestring of length 32, so our hash must meet this condition
+        assert len(signature) == 65
+        assert legendreCheck(int.from_bytes(signature[0:32], 'big'))
+        hint = signature[-1] - chaincode
+        pk = secp256k1.PublicKey(flags=secp256k1.ALL_FLAGS)
+        recover_sig = pk.ecdsa_recoverable_deserialize(signature[:-1], hint)
+        pk.public_key = pk.ecdsa_recover(hash, recover_sig, raw=True)
+        pub = pk.serialize(compressed=False)[1:]
+        assert len(pub) == 64
+        return pub
+
+    def pubToAddress(pubkey: str) -> str:
+	'''
+	Converts a public key into a hex String
+	ethereumjs-util equivalent: https://github.com/ethereumjs/ethereumjs-util/blob/master/docs/index.md#buffertohex
+	'''
+        return '0x' + (keccak(pubkey[0:])[12:]).hex()
+
+
     def isHexStrictBytes32(self, hex: str) -> bool:
         '''
         Check if a string is a hex byte
@@ -315,3 +360,17 @@ def resultToArray(self, obj: Any) -> List[Any]:
         for i in range(len(obj)):
             result.append(obj[i])
         return result
+
+    def isValidSignatureForSolidity(self, signature: str, hash: str, payee: str) -> bool:
+	'''
+	Check if the provided signature is valid for Solidity
+	:param signature: Ethereum signature
+	:param hash: transaction message hash
+	:param payee: payee address
+	'''
+        try:
+            pubkey = ecrecoverToPub(hash, signature) # if transaction message is not already hashed then use hash = messageHash(message)
+            return payee == pubToAddress(pubkey)
+        except:
+            return False
+