Swift
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Objective-C-Bridging-Header.h
#import <CommonCrypto/CommonCrypto.h>
String.swift
extension String {

    var MD5: String? {
        let length = Int(CC_MD5_DIGEST_LENGTH)
        var digest = [UInt8](repeating: 0, count: length)

        if let d = self.data(using: .utf8) {
            _ = d.withUnsafeBytes { (body: UnsafePointer<UInt8>) in
                CC_MD5(body, CC_LONG(d.count), &digest)
            }
        }

        return (0 ..< length).reduce("") {
            $0 + String(format: "%02x", digest[$1])
        }
    }

}

http://stackoverflow.com/questions/24123518/how-to-use-cc-md5-method-in-swift-language