How to decrypt via AES-GCM?

[houmie]

Hello,

Thank you for this great project. We have a bit of difficulties using AES-GCM with this library.

I have written this function in Swift to decrypt a string:

static func decryptGCM(data: String) -> String? {
        guard let combinedData = Data(base64Encoded: data) else {
            LogService.shared.logCritical("EncryptionUtil - Failed to decode base64 data.")
            return nil
        }

        let iv = combinedData[..<12]
        let tag = combinedData[12..<28]
        let encryptedData = combinedData[28...]

        LogService.shared.logCritical("EncryptionUtil - IV: \(iv.base64EncodedString())")
        LogService.shared.logCritical("EncryptionUtil - Tag: \(tag.base64EncodedString())")
        LogService.shared.logCritical("EncryptionUtil - Encrypted Data: \(encryptedData.base64EncodedString())")

        let keyString = DeviceService.shared.getTokenForConfig()
        guard let keyData = Data(base64Encoded: keyString) else {
            LogService.shared.logCritical("EncryptionUtil - Failed to decode base64 key.")
            return nil
        }

        LogService.shared.logCritical("EncryptionUtil - Key Data: \(keyData.base64EncodedString())")

        // Check the lengths of the IV and tag
        guard iv.count == 12, tag.count == 16 else {
            LogService.shared.logCritical("EncryptionUtil - Incorrect IV or Tag length.")
            return nil
        }

        do {
            let gcm = GCM(iv: [UInt8](iv), authenticationTag: [UInt8](tag), mode: .combined)
            let aes = try AES(key: [UInt8](keyData), blockMode: gcm, padding: .noPadding)

            let decryptedData = try aes.decrypt([UInt8](encryptedData))
            return String(bytes: decryptedData, encoding: .utf8)
        } catch let error {
            LogService.shared.logCritical("EncryptionUtil - Decryption failed with error: \(error)")
            return nil
        }
    }

When it reaches the let gcm = GCM( ... ) it crashes with the error: Thread 4: EXC_BAD_ACCESS (code=1, address=0x0)

I tried to run it even on main thread without any joy. I'm not sure what I'm doing wrong.