Java Crypto Libraries

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Java Crypto Libraries
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Cryptography in Java
JCA, Bouncy Castle and Web3j:Hashes, ECC and ECDSA
JCA, Bouncy Castle and Web3j
Cryptography in Java is based on the Java Cryptography Architecture (JCA)
Typical Java style: lot of boilerplate code
Bouncy Castle is the leading Java cryptography library
Docs: https://www.bouncycastle.org/documentation.html​
Web3j – a simplified library for Ethereum and secp256k1
Web3j – https://github.com/web3j​
The cryptographic functionality is in web3j/crypto
ECDSA in Java: Install the Crypto Libraries
This Maven dependency will install the following libraries:
org.web3j.crypto– Ethereum style secp256k1 EC cryptography
org.bouncycastle– BouncyCastle crypto provider for Java
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<dependency>
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  <groupId>org.web3j</groupId>
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  <artifactId>crypto</artifactId>
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  <version>3.3.1</version>
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</dependency>
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ECDSA in Java: Initialize the Application
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import org.bouncycastle.util.encoders.Hex;
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import org.web3j.crypto.*;
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import java.math.BigInteger;
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ECDSA in Java: Generate / Load Keys
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// Generate random private key
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// BigInteger privKey = Keys.createEcKeyPair().getPrivateKey(); 
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​
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BigInteger privKey = new BigInteger(
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 "97ddae0f3a25b92268175400149d65d6887b9cefaf28ea2c078e05cdc15a3c0a", 16);
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BigInteger pubKey = Sign.publicKeyFromPrivate(privKey);
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ECKeyPair keyPair = new ECKeyPair(privKey, pubKey);
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​
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System.out.println("Private key: " + privKey.toString(16));
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System.out.println("Public key: " + pubKey.toString(16));
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System.out.println("Public key (compressed): " +
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  compressPubKey(pubKey));
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ECDSA in Java: Sign Message
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String msg = "Message for signing";
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byte[] msgHash = Hash.sha3(msg.getBytes());
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Sign.SignatureData signature =
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  Sign.signMessage(msgHash, keyPair, false);
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​
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System.out.println("Msg: " + msg);
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System.out.println("Msg hash: " + Hex.toHexString(msgHash));
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System.out.printf(
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  "Signature: [v = %d, r = %s, s = %s]\n",
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  signature.getV() - 27,
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  Hex.toHexString(signature.getR()),
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  Hex.toHexString(signature.getS()));
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ECDSA in Java: Verify Signature
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BigInteger pubKeyRecovered =
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  Sign.signedMessageToKey(msg.getBytes(), signature);
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System.out.println("Recovered public key: " +
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  pubKeyRecovered.toString(16));
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​
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boolean validSig = pubKey.equals(pubKeyRecovered);
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System.out.println("Signature valid? " + validSig);
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C# Crypto Libraries

Conclusion

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Contents

Java Crypto Libraries

Cryptography in Java

JCA, Bouncy Castle and Web3j

ECDSA in Java: Install the Crypto Libraries

ECDSA in Java: Initialize the Application

ECDSA in Java: Generate / Load Keys

ECDSA in Java: Sign Message

ECDSA in Java: Verify Signature