Hi Bernd, thank you for the feedback!
On 01/25/2018 12:30 PM, Bernd Eckenfels wrote:
You Hello,
The spec should most likely mention AAD data as well and the 12 Byte
size of the nonce. And that the plaintext Limit is in blocks (and the
AAD Limit is a 64Bit counter)
Good point about AAD. My code currently doesn't check to make sure the
total AAD from each AAD update doesn't overflow the 64-bit length. It
definitely needs to and can be done pretty easily. Thanks for pointing
that out.
In terms of nonce length checking, I'll have to handle it multiple
ways. For ChaCha20ParameterSpec, I can check it in the constructor and
that's easy to do. Because ChaCha20-Poly1305 will use IvParameterSpec,
a check will need to be done in the init call. If I handle it there I
could avoid it in the ChaCha20ParameterSpec too, but it seems better to
report an error sooner rather than later and I don't think it hurts to
have the check in both places.
I will probably also need a similar check in ChaCha20Parameters when
AP.init() is called with whatever encoding we're going with.
(And yes there is no wrapping to be found, not even in RFC 8103 which
discusses key transport,)
Thanks for confirming our suspicions so far.
Does it need to define what AP.getEncoded() format/OID looks like?
Let me work backward from your two points:
Are you referring to the use of an OID instead of a name for use with
AP.getInstance()? If so I'll need to look that up, but I agree that it
needs to be called out in the specification. Thank you for pointing
that out.
Should we call out the encoding format?
It should. I would expect the output for ChaCha20-Poly1305 to just be a
DER-encoded OCTET STRING, so it would look something like
0x04 0x0C [insert 12 bytes here]
ChaCha20 is the one that concerns me, because I see no standardized
encoding. There are other algs that do SEQUENCES of octet strings and
integers in varying orders, but of course the meanings of those differ.
The ASN.1 that I'm currently encoding (because I wanted *something*) is:
SEQUENCE {
OCTET STRING (12 byte nonce)
INTEGER (initial counter value)
}
What worries me a bit is what alg name to assign to it in the standard
names document. If I call it "ChaCha20" and then some standardized
format is developed, then we have a potential conflict down the line as
we make our AP conform to the new standard. If I come up with another
name (call it "FooFoo20" as a placeholder), then getEncoded("FooFoo20")
could continue to provide that encoding into the future and leave room
for a standardized encoding with the name "ChaCha20". But what of the
default? Without a standardized format, does FooFoo20 become the
default? And when the standardized version becomes real then the
default probably should change to ChaCha20's encoding and we have
another behavioral change there. Neither of those alternatives really
sit well with me. I admit I don't have a good answer yet on this one.
--Jamil
Gruss
Bernd
--
http://bernd.eckenfels.net
_____________________________
From: Jamil Nimeh <jamil.j.ni...@oracle.com>
Sent: Donnerstag, Januar 25, 2018 6:31 PM
Subject: Proposal: ChaCha20 and ChaCha20-Poly1305 Cipher implementations
To: OpenJDK Dev list <security-dev@openjdk.java.net>
Hello all,
This is a proposal to introduce the ChaCha20 and ChaCha20-Poly1305
cipher implementations into JDK. At a high level, the plan is to
include both ChaCha20-Poly1305 and the base ChaCha20 stream cipher
into JDK as part of the SunJCE provider initially, and then add TLS
cipher suites as a follow-on feature.
Both algorithms will be CipherSpi implementations and will generally
conform to the details of that API. I will discuss below some of the
details such as which flavors of init are supported, etc.
* Instantiation
o For ChaCha20 and ChaCha20-Poly1305, the simple name will
suffice: either "ChaCha20" for the basic stream cipher or
"ChaCha20-Poly1305" for AEAD mode will work. You may however
use the 3-element transform "ChaCha20/None/NoPadding" and
"ChaCha20-Poly1305/None/NoPadding". Any other type of
transformation string will cause NoSuchAlgorithmException to
be thrown.
* Initialization
o All three engineInit methods in the CipherSpi API will be
supported. Keys provided through the various Cipher init
methods should have the algorithm String "ChaCha20" applied to
it (case-insensitive).
o For init/engineInit methods that take an
AlgorithmParameterSpec, ChaCha20 and ChaCha20-Poly1305 use
different APS classes.
+ ChaCha20 will have a new ChaCha20ParameterSpec which takes
a nonce (byte[]) and a counter (int). This class will
have getter methods to return those values if desired
(getNonce() and getBlockCounter(), respectively).
+ ChaCha20-Poly1305 will use IvParameterSpec to provide the
nonce. The primary reason this is being used instead of
ChaCha20ParameterSpec is in order to make backporting to
earlier JDK releases possible. Also there's no need to
set a counter value, so it would end up being an ignored
parameter.
+ For init calls where no AlgorithmParameterSpec or
AlgorithmParameter has been provided, a random nonce will
be set at initialization time. the counter value will be
set to 1. The random nonce can be retrieved using the
getIV() Cipher method or by using the getParameters() call
and parsing the output from AlgorithmParameters.getEncoded().
* Use
o ChaCha20 encrypt and decrypt operations would work as any
stream cipher would - as many bytes of ciphertext are returned
from an encrypt function as plaintext bytes submitted (and
vice versa for decrypt).
o ChaCha20-Poly1305 operates in a similar fashion to other AEAD
ciphers. For encryption operations, as many bytes are
returned as input submitted with the exception of the doFinal
calls, which would return any remaining ciphertext plus an
extra 16 bytes for the tag. For decryption, individual update
calls return no plaintext. The plaintext is returned only
after the last bytes of ciphertext are provided, the
authentication tag is provided, and the doFinal call is made.
Once the authentication tag has been verified then the
plaintext will be returned.
o The getOutputSize call will return the following
+ ChaCha20: Same value as the submitted input size
+ ChaCha20-Poly1305: For encrypt, the returned size will be
the input size + 16 bytes for the tag. For decryption,
the returned size will be input length - 16 bytes, or zero
(whichever is larger).
o Wrap and Unwrap: I have not been able to find a standardized
wrap/unwrap format for ChaCha20 similar to RFC 3394 for AES.
Right now the wrap() and unwrap() methods just take the
encoding of the key to be wrapped and encrypts or decrypts
them respectively. If anyone is aware of a wrapping format
for ChaCha20 please let me know. My searches have so far come
up empty.
o Counter rollover protection will be enforced. For ChaCha20
and ChaCha20-Poly1305, the cipher will cease to process input
once the 32-bit counter space has been exhausted.
o Nonce reuse protection: For both ChaCha20 and
ChaCha20-Poly1305: we will not allow reuse of the same nonce
between two consecutive init() operations.
* KeyGenerator
o There will be a new KeyGenerator algorithm called "ChaCha20"
which will create a 32-byte key suitable for use in either
ChaCha20 or ChaCha20-Poly1305 cipher instances. If you use
forms of the KeyGenerator.init() that take a variable key
length and you do something other than 32 bytes then you'll
have InvalidParameterException thrown at you.
o If you use a form of the init that takes an
AlgorithmParameterSpec it will throw
InvalidAlgorithmParameterSpecException. This is similar in
behavior to other KeyGenerators like the HmacSHA-2 family,
ARCFOUR, RC2, and AES.
* Other TBD/in-progress items
o ChaCha20Parameters: This will be added to
com.sun.crypto.provider and will be able to provide an
encoding for parameters used in ChaCha20 and ChaCha20-Poly1305
ciphers.
+ For ChaCha20-Poly1305, the default encoded form of the
AlgorithmParameters will be the AEADChaCha20Poly1305Nonce
from RFC 8103 section 3 (basically the nonce as an ASN.1
OCTET STRING of 12 bytes).
+ For ChaCha20 I have not been able to find a standardized
encoding for ChaCha20 parameters. For lack of an official
format I currently have it encoding the parameters as a
SEQUENCE of an OCTET STRING (the nonce) and an INTEGER
(the counter starting value).
# Question: If a getParameters call on a cipher is
called after the cipher has been in use for some time,
should such an encoding provide the counter's current
value, or the starting value at the time the cipher
was initialized?
* Backporting
o We would like to backport this, but because we need the new
ChaCha20ParameterSpec class to set the initial counter value
ChaCha20 will not get backported.
o ChaCha20-Poly1305 however can be backported, and the use of
IvParameterSpec with ChaCha20-Poly1305 will allow this to
happen. Being able to backport ChaCha20-Poly1305 also allows
the TLS cipher suites to be backported when those get added
(see below).
o Questions concerning how far back this will be backported and
in what timeframes are still TBD.
* Things that will not be part of this proposal...
o TLS Cipher suites: Yes, we will do this, but this will be done
as follow-on work. This proposal covers just the JCA
portion. I've already got
TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256,
TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305_SHA256, and
TLS_DHE_RSA_WITH_CHACHA20_POLY1305_SHA256 cipher suites
working, so worry not! It is our plan to have these in JSSE.
Thanks to everyone who has provided feedback so far and let's set a
closure date on the discussion for two weeks from now. I think we
should be able to hammer out any questions/concerns within that timeframe.
--Jamil
