commoncrypto.swift

import Foundation

func doIt() {
    let s = "The quick brown fox jumps over the lazy dog."
    let n = Int(CC_MD5_DIGEST_LENGTH)
    let len = CC_LONG(s.utf8.count)

    let ctx = UnsafeMutablePointer<CC_MD5_CTX>.alloc(1)
    var digest = Array<UInt8>(count:n, repeatedValue:0)

    CC_MD5_Init(ctx)
    CC_MD5_Update(ctx, s, len)
    CC_MD5_Final(&digest, ctx)
    ctx.dealloc(1)

    let hL = digest.map { String(format:"%02x", $0) }
    print(hL.reduce("", combine: +))
}

There is no need to allocate CC_MD5_CTX.

var ctx = CC_MD5_CTX()  
var digest = Array<UInt8>.init(repeating: 0, count: Int(CC_MD5_DIGEST_LENGTH))  
CC_MD5_Init(&ctx)  
CC_MD5_Update(&ctx, s, CC_LONG(s.utf8.count))  
CC_MD5_Final(&digest, &ctx)