很多时候我们会用到md5加密，下面是swift 3.0的实现方法：

首先新建桥接文件xx-Bridging-Header，方法很多，最简单的办法是在swift工程中任意新建一个oc文件，然后会自动提示创建。

然后在桥接文件中引入加密库

//
//  Use this file to import your target's public headers that you would like to expose to Swift.
//

#import <CommonCrypto/CommonDigest.h>

加密拓展类为StringMd5.swift

import Foundation

extension String {
    func md5() -> String {
        let str = self.cString(using: String.Encoding.utf8)
        let strLen = CUnsignedInt(self.lengthOfBytes(using: String.Encoding.utf8))
        let digestLen = Int(CC_MD5_DIGEST_LENGTH)
        let result = UnsafeMutablePointer<CUnsignedChar>.init(allocatingCapacity: digestLen)
        CC_MD5(str!, strLen, result)
        let hash = NSMutableString()
        for i in 0 ..< digestLen {
            hash.appendFormat("%02x", result[i])
        }
        result.deinitialize()
        
        return String(format: hash as String)
    }
}

接下来只需要调用就可以了：

let md5String = someString.md5()

资料：
[http://stackoverflow.com/questions/28310589/decode-a-string-in-swift]
[http://stackoverflow.com/questions/24123518/how-to-use-cc-md5-method-in-swift-language]