Password Based Key Derivation Calibration Swift 3

Determine the number of PRF rounds to use for a specific delay on the current platform.

Several parameters are defaulted to representative values that should not materially affect the round count.

password Sample password.  
salt     Sample salt.  
msec     Targeted duration we want to achieve for a key derivation.

returns  The number of iterations to use for the desired processing time.

func pbkdf2SHA1Calibrate(password: String, salt: Data, msec: Int) -> UInt32 {
    let actualRoundCount: UInt32 = CCCalibratePBKDF(
        CCPBKDFAlgorithm(kCCPBKDF2),
        password.utf8.count,
        salt.count,
        CCPseudoRandomAlgorithm(kCCPRFHmacAlgSHA1),
        kCCKeySizeAES256,
        UInt32(msec));
    return actualRoundCount
}

Example usage:

let saltData       = Data(bytes: [0x73, 0x61, 0x6c, 0x74, 0x44, 0x61, 0x74, 0x61])
let passwordString = "password"
let delayMsec      = 100

let rounds = pbkdf2SHA1Calibrate(password:passwordString, salt:saltData, msec:delayMsec)
print("For \(delayMsec) msec delay, rounds: \(rounds)")

Example Output:

For 100 msec delay, rounds: 93457

Found a mistake? Have a question or improvement idea? Let me know.

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