由于没有“sha-2”这样的东西，所以到底需要哪种散列并不清楚。假设sha-2表示SHA-2系列散列函数，常见的选择是SHA-256和SHA-512。
使用普通Crypoto（Swift 2）的示例

func sha256(string: String) -> [UInt8] {
    var digest = [UInt8](count: Int(CC_SHA256_DIGEST_LENGTH), repeatedValue: 0)
    if let data = string.dataUsingEncoding(NSUTF8StringEncoding) {
        CC_SHA256(data.bytes, CC_LONG(data.length), &digest)
    }
    return digest
}

测试

let testString = "testString"
let testHash = sha256(testString)
print("testHash: \(testHash)")

let testHashNSData = NSData(bytes:testHash, length:testHash.count)
print("testHashNSData: \(testHashNSData)")

let testHashBase64 = testHashNSData.base64EncodedStringWithOptions([])
print("testHashBase64: \(testHashBase64)")

输出量：

testHash: [74, 207, 11, 57, 217, 196, 118, 103, 9, 163, 104, 159, 85, 58, 192, 26, 181, 80, 84, 95, 250, 69, 68, 223, 192, 178, 206, 168, 47, 186, 2, 163]
testHashNSData: <4acf0b39 d9c47667 09a3689f 553ac01a b550545f fa4544df c0b2cea8 2fba02a3>
testHashBase64: Ss8LOdnEdmcJo2ifVTrAGrVQVF/6RUTfwLLOqC+6AqM=

使用普通Crypoto（Swift 3）的示例

func sha256(string: String) -> Data? {
    let messageData = string.data(using:String.Encoding.utf8)!
    var digestData = Data(count: Int(CC_SHA256_DIGEST_LENGTH))

    _ = digestData.withUnsafeMutableBytes {digestBytes in
        messageData.withUnsafeBytes {messageBytes in
            CC_SHA256(messageBytes, CC_LONG(messageData.count), digestBytes)
        }
    }
    return digestData
}

测试

let testString = "testString"
let testHash = sha256(string:testString)
print("testHash: \(testHash!.map { String(format: "%02hhx", $0) }.joined())")

let testHashBase64 = testHash!.base64EncodedString()
print("testHash: \(testHasBase64)")

输出量：

testHash: 4acf0b39d9c4766709a3689f553ac01ab550545ffa4544dfc0b2cea82fba02a3  
testHashBase64: Ss8LOdnEdmcJo2ifVTrAGrVQVF/6RUTfwLLOqC+6AqM=

注：添加到桥接标题：

# import <CommonCrypto/CommonCrypto.h>