I want to use AES-GCM encryption of a plaintext with 'key' only. The 'key' will be received from backend (.net), in webservice response. The same key will be used later in backend as well to decrypt the encrypted value.

I have used extension as follwoing

To generate string to Symetric key

extension SymmetricKey {
init(string keyString: String, size: SymmetricKeySize = .bits256) throws {
guard var keyData = keyString.data(using: .utf8) else {
print("Could not create base64 encoded Data from String.")
throw CryptoKitError.incorrectParameterSize
}

let keySizeBytes = size.bitCount / 8
keyData = keyData.subdata(in: 0..= keySizeBytes else { throw CryptoKitError.incorrectKeySize }
self.init(data: keyData)
} }

Encryption & Decryption code snipet:

func aesgcmEncryptDecrypt() {
let str : String = "FwhXRYJ$xLf?^Kh6_&YfTJ%RuG+EqcTY"
var key : SymmetricKey = SymmetricKey(size: .bits256)
do{
key = try SymmetricKey(string: str)
}catch{
}
let plain = "HOW ARE YOU?"
let nonce = try! AES.GCM.Nonce(data: Data(base64Encoded: "fv1nixTVoYpSvpdA")!)
let tag = Data(base64Encoded: "e1eIgoB4+lA/j3KDHhY4BQ==")!
// Encrypt
let sealedBox = try! AES.GCM.seal(plain.data(using: .utf8)!, using: key,
nonce: nonce, authenticating: tag)
// Decrypt
let sealedBoxRestored = try! AES.GCM.SealedBox(combined: sealedBox.combined!)
let decrypted = try! AES.GCM.open(sealedBoxRestored, using: key,
authenticating: tag)
Swift.print("Combined:\n\(sealedBox.combined!.base64EncodedString())\n")
Swift.print("Cipher:\n\(sealedBox.ciphertext.base64EncodedString())\n")
Swift.print("Nonce:\n\(nonce.withUnsafeBytes {
Data(Array($0)).base64EncodedString() })\n")
Swift.print("Tag:\n\(tag.base64EncodedString())\n")
Swift.print("Decrypted:\n\(String(data: decrypted, encoding: .utf8)!)\n")
}
Our(generated from this code & .Net code) encrypted text is not matching. Anyone can help me, what I am doing wrong, detailing will be more helpful. Basically I was looking for saloution in Objective-C but I did not get any supported library for Objective-C.