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Practical Cryptography for Developers
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Practical Cryptography for Developers
Welcome
Preface
Cryptography - Overview
Hash Functions
MAC and Key Derivation
Secure Random Generators
Key Exchange and DHKE
Encryption: Symmetric and Asymmetric
Symmetric Key Ciphers
Asymmetric Key Ciphers
Digital Signatures
Quantum-Safe Cryptography
More Cryptographic Concepts
Crypto Libraries for Developers
JavaScript Crypto Libraries
Python Crypto Libraries
C# Crypto Libraries
Java Crypto Libraries
Conclusion
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Java Crypto Libraries

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
    Web3j – a simplified library for Ethereum and secp256k1

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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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