Bug#860771: ITP: node-diffie-hellman -- pure js diffie-hellman

[Calvin Metcalf]

So just some background, browserify is a bundler that converts JS written
for node into JS that works in the browser, it includes JS versions of
standard library in case you try to bundle libraries that use the standard
library. These standard library shims are also used by webpack.

As for diffie-helmen in specific, It's performance is not great so I highly
doubt much/any code was using it, much of the stuff using diffie-helmen in
node is connected to tls implementation and thus isn't going to be part of
something being bundled in the browser so if you have questions on it you
could probably go ahead and just remove it in favor of a stub package.

Bug#860771: ITP: node-diffie-hellman -- pure js diffie-hellman

[Christian Seiler]

On 04/20/2017 11:09 AM, Bastien ROUCARIES wrote:
> I have planned to add a big fat warning about safety of
> browserify-crypto. I am myself unease to use it but it is needed for
> browserify.
> 
> Do you prefer a README.debian per pure js crypto package ?

Maybe also add something along the lines of

| For security considerations of this package please consult
| README.Debian.

to the package's extended description? (Or is that against
policy?)

> I plan to patch browserify and add a flag in order to use the crypto API.

Isn't browserify a JS minifier? Why would that need DH key
exchange anyway? I'm a bit confused here...

Regards,
Christian

Bug#860771: ITP: node-diffie-hellman -- pure js diffie-hellman

[Bastien ROUCARIES]

On Thu, Apr 20, 2017 at 12:41 AM, Christian Seiler  wrote:
> On 04/19/2017 11:36 PM, Bastien ROUCARIES wrote:
>> Package: wnpp
>> Severity: wishlist
>> Owner: ro...@debian.org
>> X-Debbugs-CC: debian-de...@lists.debian.org
>>
>> * Package name: node-diffie-hellman
>>   Version : 5.0.2
>>   Upstream Author : Calvin Metcalf
>> * URL : https://github.com/crypto-browserify/diffie-hellman
>> * License : Expat
>>   Programming Lang: JavaScript
>>   Description : pure js diffie-hellman key exchange
>>
>>  Diffie–Hellman key exchange (D–H)  is a specific method of securely
>>  exchanging cryptographic keys over a public channel. The
>> Diffie–Hellman key exchange method allows two parties that have no
>> prior knowledge of each other to jointly establish a shared secret key
>> over an insecure channel. This key can then be used to encrypt
>> subsequent communications using a symmetric key cipher.
>>  .
>>  Node.js is an event-based server-side JavaScript engine.
>
> Is this timing safe? From the github page it uses a pure-JS
> BigNum implementation (bn.js) for the complicated stuff, but
> the README of that code doesn't mention timing at all. And
> from perusing the source code of bn.js, it doesn't appear to
> be the case that their implementation of exponentiation in
> a prime field is geared towards constant-time execution (when
> the sizes are the same).
>
> If you look at e.g. OpenSSL's source code (bn_exp.c), there's
> a specific function (bn_mod_exp_mont_consttime) in there that
> takes great care of making sure that the operation runs in
> constant time - down to how the memory layout is organized. I
> wouldn't know how you'd even do that in an interpreted
> language such as JavaScript, but even if that's possible, I'd
> suspect that a lot of brain power would need to go into
> designing that [1], while bn.js's implementation of the
> Red.pow function seems rather straight-forward. (Which is
> fine, bn.js appears to have the goal to be a generic bignum
> library, and not targeted at crypto.)
>
> What I'm saying is: while not having tested that, I believe
> that this implementation of DH is going to be susceptible to
> timing attacks. (And if it isn't, the author should really
> provide some rationale why not, with some test results. The
> README is rather sparse, though.) Which would be fine if you
> just wanted to use this library to generate the DH prime
> itself (that is not timing critical), or just use it in an
> academic context (to let people play around with DH), but
> I'd not want to use this for real-world applications of the
> actual key exchange protocol.

I have planned to add a big fat warning about safety of
browserify-crypto. I am myself unease to use it but it is needed for
browserify.

Do you prefer a README.debian per pure js crypto package ?

I plan to patch browserify and add a flag in order to use the crypto API.



>
> Regards,
> Christian
>
> [1] Especially if this is to be run in browsers, with
> different JITs etc. Designing algorithms in pure JS
> for these environments that are timing-safe looks rather
> daunting to me.

Bug#860771: ITP: node-diffie-hellman -- pure js diffie-hellman

[Christian Seiler]

On 04/19/2017 11:36 PM, Bastien ROUCARIES wrote:
> Package: wnpp
> Severity: wishlist
> Owner: ro...@debian.org
> X-Debbugs-CC: debian-de...@lists.debian.org
> 
> * Package name: node-diffie-hellman
>   Version : 5.0.2
>   Upstream Author : Calvin Metcalf
> * URL : https://github.com/crypto-browserify/diffie-hellman
> * License : Expat
>   Programming Lang: JavaScript
>   Description : pure js diffie-hellman key exchange
> 
>  Diffie–Hellman key exchange (D–H)  is a specific method of securely
>  exchanging cryptographic keys over a public channel. The
> Diffie–Hellman key exchange method allows two parties that have no
> prior knowledge of each other to jointly establish a shared secret key
> over an insecure channel. This key can then be used to encrypt
> subsequent communications using a symmetric key cipher.
>  .
>  Node.js is an event-based server-side JavaScript engine.

Is this timing safe? From the github page it uses a pure-JS
BigNum implementation (bn.js) for the complicated stuff, but
the README of that code doesn't mention timing at all. And
from perusing the source code of bn.js, it doesn't appear to
be the case that their implementation of exponentiation in
a prime field is geared towards constant-time execution (when
the sizes are the same).

If you look at e.g. OpenSSL's source code (bn_exp.c), there's
a specific function (bn_mod_exp_mont_consttime) in there that
takes great care of making sure that the operation runs in
constant time - down to how the memory layout is organized. I
wouldn't know how you'd even do that in an interpreted
language such as JavaScript, but even if that's possible, I'd
suspect that a lot of brain power would need to go into
designing that [1], while bn.js's implementation of the
Red.pow function seems rather straight-forward. (Which is
fine, bn.js appears to have the goal to be a generic bignum
library, and not targeted at crypto.)

What I'm saying is: while not having tested that, I believe
that this implementation of DH is going to be susceptible to
timing attacks. (And if it isn't, the author should really
provide some rationale why not, with some test results. The
README is rather sparse, though.) Which would be fine if you
just wanted to use this library to generate the DH prime
itself (that is not timing critical), or just use it in an
academic context (to let people play around with DH), but
I'd not want to use this for real-world applications of the
actual key exchange protocol.

Regards,
Christian

[1] Especially if this is to be run in browsers, with
different JITs etc. Designing algorithms in pure JS
for these environments that are timing-safe looks rather
daunting to me.

Bug#860771: ITP: node-diffie-hellman -- pure js diffie-hellman

[Bastien ROUCARIES]

Package: wnpp
Severity: wishlist
Owner: ro...@debian.org
X-Debbugs-CC: debian-de...@lists.debian.org

* Package name: node-diffie-hellman
  Version : 5.0.2
  Upstream Author : Calvin Metcalf
* URL : https://github.com/crypto-browserify/diffie-hellman
* License : Expat
  Programming Lang: JavaScript
  Description : pure js diffie-hellman key exchange

 Diffie–Hellman key exchange (D–H)  is a specific method of securely
 exchanging cryptographic keys over a public channel. The
Diffie–Hellman key exchange method allows two parties that have no
prior knowledge of each other to jointly establish a shared secret key
over an insecure channel. This key can then be used to encrypt
subsequent communications using a symmetric key cipher.
 .
 Node.js is an event-based server-side JavaScript engine.