Swift - Generate SHA256

extension String {

	func sha256() -> String {
		if let stringData = self.data(using: String.Encoding.utf8) {
			return hexStringFromData(input: digest(input: stringData as NSData))
		}
		return ""
	}

	private func digest(input: NSData) -> NSData {
		let digestLength = Int(CC_SHA256_DIGEST_LENGTH)
		var hash = [UInt8](repeating: 0, count: digestLength)
		CC_SHA256(input.bytes, UInt32(input.length), &hash)
		return NSData(bytes: hash, length: digestLength)
	}

	private  func hexStringFromData(input: NSData) -> String {
		var bytes = [UInt8](repeating: 0, count: input.length)
		input.getBytes(&bytes, length: input.length)

		var hexString = ""
		for byte in bytes {
			hexString += String(format: "%02x", UInt8(byte))
		}

		return hexString
	}

}