RUSTSEC-2019-0029 ChaCha20 counter overflow can expose repetitions in the keystream

The ChaCha20 stream cipher can produce a maximum of 2^32 blocks 256GB before the 32-bit counter overflows. Releases of the chacha20 crate prior to v0.2.3 allow generating keystreams larger than this, including seeking past the limit. When this occurs, the keystream is duplicated, with failure mod...