Merge branch 'master' into count_leading_0s_new_algo

Author: Hardvan

.github/workflows/build.yml

@@ -10,7 +10,7 @@ jobs:
         uses: actions/setup-java@v4
         with:
           java-version: 21
-          distribution: 'adopt'
+          distribution: 'temurin'
       - name: Build with Maven
         run: mvn --batch-mode --update-snapshots verify
       - name: Upload coverage to codecov (tokenless)

.github/workflows/codeql.yml

@@ -30,7 +30,7 @@ jobs:
         uses: actions/setup-java@v4
         with:
           java-version: 21
-          distribution: 'adopt'
+          distribution: 'temurin'
 
       - name: Initialize CodeQL
         uses: github/codeql-action/init@v3

.github/workflows/infer.yml

@@ -18,7 +18,7 @@ jobs:
         uses: actions/setup-java@v4
         with:
           java-version: 21
-          distribution: 'adopt'
+          distribution: 'temurin'
 
       - name: Set up OCaml
         uses: ocaml/setup-ocaml@v3

DIRECTORY.md

@@ -0,0 +1,71 @@
+package com.thealgorithms.ciphers;
+
+/**
+ * The Atbash cipher is a simple substitution cipher that replaces each letter
+ * in the alphabet with its reverse.
+ * For example, 'A' becomes 'Z', 'B' becomes 'Y', and so on. It works
+ * identically for both uppercase and lowercase letters.
+ * It's a symmetric cipher, meaning applying it twice returns the original text.
+ * Hence, the encrypting and the decrypting functions are identical
+ * @author https://github.com/Krounosity
+ * Learn more: https://en.wikipedia.org/wiki/Atbash
+ */
+
+public class AtbashCipher {
+
+    private String toConvert;
+
+    // Default constructor.
+    AtbashCipher() {
+    }
+
+    // String setting constructor.
+    AtbashCipher(String str) {
+        toConvert = str;
+    }
+
+    // String getter method.
+    public String getString() {
+        return toConvert;
+    }
+
+    // String setter method.
+    public void setString(String str) {
+        toConvert = str;
+    }
+
+    // Checking whether the current character is capital.
+    private boolean isCapital(char ch) {
+        return ch >= 'A' && ch <= 'Z';
+    }
+
+    // Checking whether the current character is smallcased.
+    private boolean isSmall(char ch) {
+        return ch >= 'a' && ch <= 'z';
+    }
+
+    // Converting text to atbash cipher code or vice versa.
+    public String convert() {
+
+        // Using StringBuilder to store new string.
+        StringBuilder convertedString = new StringBuilder();
+
+        // Iterating for each character.
+        for (char ch : toConvert.toCharArray()) {
+
+            // If the character is smallcased.
+            if (isSmall(ch)) {
+                convertedString.append((char) ('z' - (ch - 'a')));
+            }
+            // If the character is capital cased.
+            else if (isCapital(ch)) {
+                convertedString.append((char) ('Z' - (ch - 'A')));
+            }
+            // Non-alphabetical character.
+            else {
+                convertedString.append(ch);
+            }
+        }
+        return convertedString.toString();
+    }
+}

src/main/java/com/thealgorithms/ciphers/AtbashCipher.java

@@ -0,0 +1,236 @@
+package com.thealgorithms.ciphers;
+
+import java.math.BigInteger;
+import java.security.SecureRandom;
+
+/**
+ * ECC - Elliptic Curve Cryptography
+ * Elliptic Curve Cryptography is a public-key cryptography method that uses the algebraic structure of
+ * elliptic curves over finite fields. ECC provides a higher level of security with smaller key sizes compared
+ * to other public-key methods like RSA, making it particularly suitable for environments where computational
+ * resources are limited, such as mobile devices and embedded systems.
+ *
+ * This class implements elliptic curve cryptography, providing encryption and decryption
+ * functionalities based on public and private key pairs.
+ *
+ * @author xuyang
+ */
+public class ECC {
+
+    private BigInteger privateKey; // Private key used for decryption
+    private ECPoint publicKey; // Public key used for encryption
+    private EllipticCurve curve; // Elliptic curve used in cryptography
+    private ECPoint basePoint; // Base point G on the elliptic curve
+
+    public ECC(int bits) {
+        generateKeys(bits); // Generates public-private key pair
+    }
+
+    public EllipticCurve getCurve() {
+        return curve; // Returns the elliptic curve
+    }
+
+    public void setCurve(EllipticCurve curve) {
+        this.curve = curve;
+    }
+
+    // Getter and Setter for private key
+    public BigInteger getPrivateKey() {
+        return privateKey;
+    }
+
+    public void setPrivateKey(BigInteger privateKey) {
+        this.privateKey = privateKey;
+    }
+
+    /**
+     * Encrypts the message using the public key.
+     * The message is transformed into an ECPoint and encrypted with elliptic curve operations.
+     *
+     * @param message The plain message to be encrypted
+     * @return The encrypted message as an array of ECPoints (R, S)
+     */
+    public ECPoint[] encrypt(String message) {
+        BigInteger m = new BigInteger(message.getBytes()); // Convert message to BigInteger
+        SecureRandom r = new SecureRandom(); // Generate random value for k
+        BigInteger k = new BigInteger(curve.getFieldSize(), r); // Generate random scalar k
+
+        // Calculate point r = k * G, where G is the base point
+        ECPoint rPoint = basePoint.multiply(k, curve.getP(), curve.getA());
+
+        // Calculate point s = k * publicKey + encodedMessage
+        ECPoint sPoint = publicKey.multiply(k, curve.getP(), curve.getA()).add(curve.encodeMessage(m), curve.getP(), curve.getA());
+
+        return new ECPoint[] {rPoint, sPoint}; // Return encrypted message as two ECPoints
+    }
+
+    /**
+     * Decrypts the encrypted message using the private key.
+     * The decryption process is the reverse of encryption, recovering the original message.
+     *
+     * @param encryptedMessage The encrypted message as an array of ECPoints (R, S)
+     * @return The decrypted plain message as a String
+     */
+    public String decrypt(ECPoint[] encryptedMessage) {
+        ECPoint rPoint = encryptedMessage[0]; // First part of ciphertext
+        ECPoint sPoint = encryptedMessage[1]; // Second part of ciphertext
+
+        // Perform decryption: s - r * privateKey
+        ECPoint decodedMessage = sPoint.subtract(rPoint.multiply(privateKey, curve.getP(), curve.getA()), curve.getP(), curve.getA());
+
+        BigInteger m = curve.decodeMessage(decodedMessage); // Decode the message from ECPoint
+
+        return new String(m.toByteArray()); // Convert BigInteger back to String
+    }
+
+    /**
+     * Generates a new public-private key pair for encryption and decryption.
+     *
+     * @param bits The size (in bits) of the keys to generate
+     */
+    public final void generateKeys(int bits) {
+        SecureRandom r = new SecureRandom();
+        curve = new EllipticCurve(bits); // Initialize a new elliptic curve
+        basePoint = curve.getBasePoint(); // Set the base point G
+
+        // Generate private key as a random BigInteger
+        privateKey = new BigInteger(bits, r);
+
+        // Generate public key as the point publicKey = privateKey * G
+        publicKey = basePoint.multiply(privateKey, curve.getP(), curve.getA());
+    }
+
+    /**
+     * Class representing an elliptic curve with the form y^2 = x^3 + ax + b.
+     */
+    public static class EllipticCurve {
+        private final BigInteger a; // Coefficient a in the curve equation
+        private final BigInteger b; // Coefficient b in the curve equation
+        private final BigInteger p; // Prime number p, defining the finite field
+        private final ECPoint basePoint; // Base point G on the curve
+
+        // Constructor with explicit parameters for a, b, p, and base point
+        public EllipticCurve(BigInteger a, BigInteger b, BigInteger p, ECPoint basePoint) {
+            this.a = a;
+            this.b = b;
+            this.p = p;
+            this.basePoint = basePoint;
+        }
+
+        // Constructor that randomly generates the curve parameters
+        public EllipticCurve(int bits) {
+            SecureRandom r = new SecureRandom();
+            this.p = BigInteger.probablePrime(bits, r); // Random prime p
+            this.a = new BigInteger(bits, r); // Random coefficient a
+            this.b = new BigInteger(bits, r); // Random coefficient b
+            this.basePoint = new ECPoint(BigInteger.valueOf(4), BigInteger.valueOf(8)); // Fixed base point G
+        }
+
+        public ECPoint getBasePoint() {
+            return basePoint;
+        }
+
+        public BigInteger getP() {
+            return p;
+        }
+
+        public BigInteger getA() {
+            return a;
+        }
+
+        public BigInteger getB() {
+            return b;
+        }
+
+        public int getFieldSize() {
+            return p.bitLength();
+        }
+
+        public ECPoint encodeMessage(BigInteger message) {
+            // Simple encoding of a message as an ECPoint (this is a simplified example)
+            return new ECPoint(message, message);
+        }
+
+        public BigInteger decodeMessage(ECPoint point) {
+            return point.getX(); // Decode the message from ECPoint (simplified)
+        }
+    }
+
+    /**
+     * Class representing a point on the elliptic curve.
+     */
+    public static class ECPoint {
+        private final BigInteger x; // X-coordinate of the point
+        private final BigInteger y; // Y-coordinate of the point
+
+        public ECPoint(BigInteger x, BigInteger y) {
+            this.x = x;
+            this.y = y;
+        }
+
+        public BigInteger getX() {
+            return x;
+        }
+
+        public BigInteger getY() {
+            return y;
+        }
+
+        @Override
+        public String toString() {
+            return "ECPoint(x=" + x.toString() + ", y=" + y.toString() + ")";
+        }
+
+        /**
+         * Add two points on the elliptic curve.
+         */
+        public ECPoint add(ECPoint other, BigInteger p, BigInteger a) {
+            if (this.x.equals(BigInteger.ZERO) && this.y.equals(BigInteger.ZERO)) {
+                return other; // If this point is the identity, return the other point
+            }
+            if (other.x.equals(BigInteger.ZERO) && other.y.equals(BigInteger.ZERO)) {
+                return this; // If the other point is the identity, return this point
+            }
+
+            BigInteger lambda;
+            if (this.equals(other)) {
+                // Special case: point doubling
+                lambda = this.x.pow(2).multiply(BigInteger.valueOf(3)).add(a).multiply(this.y.multiply(BigInteger.valueOf(2)).modInverse(p)).mod(p);
+            } else {
+                // General case: adding two different points
+                lambda = other.y.subtract(this.y).multiply(other.x.subtract(this.x).modInverse(p)).mod(p);
+            }
+
+            BigInteger xr = lambda.pow(2).subtract(this.x).subtract(other.x).mod(p);
+            BigInteger yr = lambda.multiply(this.x.subtract(xr)).subtract(this.y).mod(p);
+
+            return new ECPoint(xr, yr);
+        }
+
+        /**
+         * Subtract two points on the elliptic curve.
+         */
+        public ECPoint subtract(ECPoint other, BigInteger p, BigInteger a) {
+            ECPoint negOther = new ECPoint(other.x, p.subtract(other.y)); // Negate the Y coordinate
+            return this.add(negOther, p, a); // Add the negated point
+        }
+
+        /**
+         * Multiply a point by a scalar (repeated addition).
+         */
+        public ECPoint multiply(BigInteger k, BigInteger p, BigInteger a) {
+            ECPoint result = new ECPoint(BigInteger.ZERO, BigInteger.ZERO); // Identity point
+            ECPoint addend = this;
+
+            while (k.signum() > 0) {
+                if (k.testBit(0)) {
+                    result = result.add(addend, p, a); // Add the current point
+                }
+                addend = addend.add(addend, p, a); // Double the point
+                k = k.shiftRight(1); // Divide k by 2
+            }
+
+            return result;
+        }
+    }
+}