如何在iOS Swift 3.1中将字符串转换为32字节数的数据

Question

如何在iOS Swift 3中将字符串转换为数据或NSData 32字节数.
我有一个这样的键:

let keyString = "hpXa6pTJOWDAClC/J6POVTjvJpMIiPAMQiTMjBrcOGw=" 

并测试此代码以转换为数据:

let keyData: Data = keyString.data(using: String.Encoding(rawValue: String.Encoding.utf8.rawValue))!  
let keyLength = keyData.count //44

密钥长度为44.
我需要转换为32,因为有效的密钥字节数应该等于:16或24或32基于这种情况:

let validKeyLengths = [kCCKeySizeAES128, kCCKeySizeAES192, kCCKeySizeAES256]

Answer 1

这是一个Base64编码的字符串,Data(base64Encoded:) 可以用来解码它,它只提供32个字节:

let keyString = "hpXa6pTJOWDAClC/J6POVTjvJpMIiPAMQiTMjBrcOGw="

if let keyData = Data(base64Encoded: keyString) {
    print(keyData.count) // 32
    print(keyData as NSData) // <8695daea 94c93960 c00a50bf 27a3ce55 38ef2693 0888f00c 4224cc8c 1adc386c>
}

根据字符串的来源,您可能需要添加.ignoreUnknownCharacters选项以忽略未知字符(包括行结束字符),如@ l'L'l所示:

if let keyData = Data(base64Encoded: keyString, options: .ignoreUnknownCharacters) { ... }