openssh unix dev - Mar 2023 - ChaCha20 Rekey Frequency

On Wed, 29 Mar 2023, Thorsten Glaser wrote:
> Hi Damien,
> 
> >This is what I'm playing with at the moment:
> 
> if you?re playing with this currently anyway, shouldn?t?
> 
> >+	/*
> >+	 * Otherwise, use the RFC4344 s3.2 recommendation of 2**(L/4) blocks
> >+	 * before rekeying where L is the blocksize in bits.
> >+	 * Most other ciphers have a 128 bit blocksize, so this equates to
> >+	 * 2**32 blocks / 64GB data.
> >+	 */
> >+	return (uint64_t)1 << (c->block_size * 2);
> 
> ? this get an upper bound? This is UB for 256-bit blocksizes
> at least?
block sizes in struct sshcipher are in bytes, not bits

On Thu, 30 Mar 2023, Damien Miller wrote:
>> >+	return (uint64_t)1 << (c->block_size * 2);
>> 
>> ? this get an upper bound? This is UB for 256-bit blocksizes
>> at least?
>
>block sizes in struct sshcipher are in bytes, not bits
Yes, exactly.

256 bit = 32 bytes; 32*2 = 64; (uint64_t)1 << 64 is UB.

bye,
//mirabilos
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