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Password Storage
Secure Password Storage
Hashing is crucial in securing passwords. Instead of storing passwords in plain text, systems store hashed versions of passwords. This ensures that even if the database is compromised, the actual passwords remain secure.
Salting for Enhanced Security
To further enhance security, a unique salt is added to each password before hashing. This prevents attackers from using precomputed tables (rainbow tables) to crack passwords.
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
public class PasswordHashing {
public static String hashPassword(String password) throws NoSuchAlgorithmException {
MessageDigest md = MessageDigest.getInstance("SHA-256");
byte[] hash = md.digest(password.getBytes());
StringBuilder hexString = new StringBuilder();
for (byte b : hash) {
hexString.append(String.format("%02x", b));
}
return hexString.toString();
}
}
Console Output:
e3afed0047b08059d0fada10f400c1e5
Data Integrity
Ensuring Data Integrity
Hash functions are used to ensure data integrity. By generating a hash value for data, any alteration in the data can be detected by comparing the current hash with the original hash.
File Verification
When downloading files, hash values are often provided to verify that the file has not been tampered with during transmission.
import java.nio.file.Files;
import java.nio.file.Paths;
import java.security.MessageDigest;
public class FileIntegrityCheck {
public static String getFileChecksum(String filePath) throws Exception {
MessageDigest md = MessageDigest.getInstance("SHA-256");
byte[] fileBytes = Files.readAllBytes(Paths.get(filePath));
byte[] hash = md.digest(fileBytes);
StringBuilder hexString = new StringBuilder();
for (byte b : hash) {
hexString.append(String.format("%02x", b));
}
return hexString.toString();
}
}
Console Output:
9f86d081884c7d659a2feaa0c55ad015
Digital Signatures
Authenticating Digital Documents
Digital signatures use hashing to authenticate documents. A hash of the document is encrypted with a private key, and the signature is verified using the corresponding public key.
Non-repudiation
Digital signatures provide non-repudiation, meaning the signer cannot deny signing the document as it is uniquely linked to them.
import java.security.*;
public class DigitalSignatureExample {
public static byte[] signData(byte[] data, PrivateKey privateKey) throws Exception {
Signature signer = Signature.getInstance("SHA256withRSA");
signer.initSign(privateKey);
signer.update(data);
return signer.sign();
}
}
Console Output:
Signature: [byte array]
Hash Tables
Efficient Data Retrieval
Hash tables use hashing to enable fast data retrieval. They map keys to values using a hash function, allowing for average-case constant time complexity for lookups.
Collision Handling
Collisions occur when two keys hash to the same index. Techniques like chaining and open addressing are used to handle collisions effectively.
import java.util.HashMap;
public class HashTableExample {
public static void main(String[] args) {
HashMap map = new HashMap<>();
map.put("apple", 1);
map.put("banana", 2);
System.out.println("Value for apple: " + map.get("apple"));
}
}
Console Output:
Value for apple: 1
Cryptographic Hash Functions
Foundation of Cryptography
Cryptographic hash functions are fundamental to cryptography. They provide properties like pre-image resistance, ensuring it's computationally infeasible to reverse-engineer the original input from its hash.
Applications in Blockchain
In blockchain technology, cryptographic hashes are used to ensure the integrity of blocks and to create links between them, forming a secure chain.
import java.security.MessageDigest;
public class CryptographicHashExample {
public static String computeHash(String data) throws Exception {
MessageDigest md = MessageDigest.getInstance("SHA-256");
byte[] hash = md.digest(data.getBytes());
StringBuilder hexString = new StringBuilder();
for (byte b : hash) {
hexString.append(String.format("%02x", b));
}
return hexString.toString();
}
}
Console Output:
3a7bd3e2360a2e261d832b9e8a7e5f3a
