RFR: ChaCha20 and ChaCha20/Poly1305 Cipher implementations

Jamil Nimeh jamil.j.nimeh at oracle.com
Tue Apr 10 21:37:24 UTC 2018

Hello Thomas, et al.,

On 3/26/2018 1:49 PM, Jamil Nimeh wrote:
> Hi Thomas, thanks for the feedback
>  1. Were there guidelines?  Not really, though I looked at other
>     parameter definitions in com.sun.crypto.provider and tried to
>     follow along the same lines that they do.  One thing that should
>     be changed is the LINE_SEP assignment shouldn't be an explicit
>     getProperty call.  I noticed most are doing System.lineSeparator()
>     so I'll change my implementation to match that.  None of these
>     params appear to stringify as json, so I'll probably keep things
>     consistent with the other parameter output.
>  2. You make a fair point with respect to a null SecureRandom. I can
>     make that spec change.
>  3. Let me think on this one - I shied away from ChaCha20ParameterSpec
>     for AEAD mode only because you have this nonce field that is set
>     but gets ignored.  But making ChaCha20ParameterSpec an
>     IvParameterSpec potentially runs into the same issue were it used
>     for a ChaCha20-Poly1305 cipher. If I had to choose between the two
>     I think I'd go with allowing ChaCha20ParameterSpec to be used with
>     CC20-P1305 rather than making it a subclass of IvParameterSpec. 
>     Doing the former helps from a type safety perspective that you
>     couldn't use a ChaCha20ParameterSpec with other Ciphers that
>     require an IvParameterSpec.  I know I had some discussions early
>     on in the design where we talked about this, I need to refresh my
>     memory as to why we didn't allow it.
Finally getting back to #3.  Took me a while to find early discussions 
on this.  The primary objection to ChaCha20ParameterSpec being used with 
ChaCha20-Poly1305 (as opposed to plain old ChaCha20) has to do with the 
configurable block counter.  You have this parameter that is not used, 
and consumption of this type of AlgorithmParameterSpec then leaves it to 
documentation to define what happens (is it ignored?  Used despite what 
the spec says?  Set to some default value regardless of what the caller 
sets there?). Using IvParameterSpec with ChaCha20-Poly1305 is more clear 
because it only allows the caller what they need to get CC20/P1305 
going, the nonce.  Respectfully, I would like to keep this as-is.
> --Jamil
> On 3/26/2018 12:45 PM, Thomas Lußnig wrote:
>> Hi Jamil,
>> 1) where there any guidelines about how the engineToString should be 
>> formatted ?
>> I ask because i wondering why we need two new lines with access to 
>> the System property.
>> If it is represented as single line json no need to line break would 
>> be needed.
>> Gruß Thomas
>> /** * Creates a formatted string describing the parameters. * * 
>> @return a string representation of the ChaCha20 parameters. */ 
>> @Override protected String engineToString() { String LINE_SEP = 
>> System.getProperty("line.separator"); HexDumpEncoder encoder = new 
>> HexDumpEncoder(); StringBuilder sb = new StringBuilder(LINE_SEP + 
>> "nonce:" + LINE_SEP + "[" + encoder.encodeBuffer(nonce) + "]"); 
>> return sb.toString(); }
>> 2) I do not think it is an good idea to say no secureRandom=null will cause IV to be null.
>>     I see here the risk of weak implementations. I would suggest to throw an Exception to
>>     enforce secure usages. If someone really want an insecure IV he can provide am SecureRandom
>>     implementation retuning 0 only or an matching IV.
>>       * @param random a {@code SecureRandom} implementation.  If {@code null}
>>       *      is used for the random object, then a nonce consisting of all
>>       *      zero bytes will be used.  Otherwise a random nonce will be
>>       *      used.
>> 3) If ChaCha20ParameterSpec would extends IvParameterSpec if would be valid for booth modes in engineInit.
>>      Even if the counter is not needed.
>>      As an alternative i would allow ChaCha20ParameterSpec also for AEAD mode.
>> Grup Thomas
>> On 3/26/2018 9:08 PM, Jamil Nimeh wrote:
>>> Hello all,
>>> This is a request for review for the ChaCha20 and ChaCha20-Poly1305 
>>> cipher implementations.  Links to the webrev and the JEP which 
>>> outlines the characteristics and behavior of the ciphers are listed 
>>> below.
>>> http://cr.openjdk.java.net/~jnimeh/reviews/8153028/webrev.01/
>>> http://openjdk.java.net/jeps/329
>>> Thanks,
>>> --Jamil

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