Added efficient hill cipher code in Swift

Cryptography/HillCipher/Swift/HillCipher.swift

@@ -0,0 +1,45 @@
+import simd
+
+let message = "ACT"
+let key = "GYBNQKURP"
+
+// Set Key Matrix
+let keyAsciiMapped = key.map { $0.asciiValue! % 65 }
+var keyMatrix = simd_float3x3()
+for i in 0..<3 {
+    for j in 0..<3 {
+        keyMatrix[i][j] = Float(keyAsciiMapped[i*3 + j])
+    }
+}
+
+// Set Message Vector
+let messageAsciiMaped = message.map { Float($0.asciiValue! % 65) }
+let messageVector = simd_float3(messageAsciiMaped)
+
+// Helper Function: get String from simd vector
+func getString(from vector: simd_float3) -> String {
+    var string = ""
+    for i in 0..<vector.scalarCount {
+        let mappedValue = Int(Float(vector[i].description)!) % 26
+        string.append(Character(UnicodeScalar(mappedValue + 65)!))
+    }
+    return string
+}
+
+// MARK: - Hill Cipher
+func hillCipher() {
+    let cipherVector = simd_mul(messageVector, keyMatrix)
+    let cipherText = getString(from: cipherVector)
+    print("Cipher Text: \(cipherText)")
+}
+
+// MARK: - Decipher
+func decipher() {
+    let message = simd_mul(messageVector, keyMatrix) * keyMatrix.inverse
+    let decipherText = getString(from: message)
+    print("Decipher Text: \(decipherText)")
+}
+
+// MARK: - Usage
+hillCipher()
+decipher()