This adds `rand_bytes(dst: []byte)` which fills the destination buffer
with entropy from the cryptographic random number generator. This takes
the "simple is best" approach and just directly returns the OS CSPRNG
output instead of doing anything fancy (a la OpenBSD's arc4random).
Linux is in the unfortunate situation where the system call number is
architecture specific. This consolidates the system call number
definitions in a single location, adds some wrappers, and hopefully
fixes the existing non-portable invocations of the syscall intrinsic.
This package implements the ChaCha20 stream cipher as specified in
RFC 8439, and the somewhat non-standard XChaCha20 variant that supports
a 192-bit nonce.
While an IETF draft for XChaCha20 standardization exists,
implementations that pre-date the draft use a 64-bit counter, instead of
the IETF-style 32-bit one. This implementation opts for the latter as
compatibility with libsodium is more important than compatibility with
an expired IETF draft.
Using a constant-time comparison is required when comparing things like
MACs, password digests, and etc to avoid exposing sensitive data via
trivial timing attacks.
These routines could also live under core:mem, but they are somewhat
specialized, and are likely only useful for cryptographic applications.
The old assembly generated for the syscall intrinsic did not specify
clobber constraints. This adds RCX and R11 (that are clobbered by
the instruction itself), and memory (that is clobbered by some
system calls) to the assembly constraints.
Note: This is still incorrect on FreeBSD, which clobbers more registers
and uses the carry flag instead of -errno in rax to indicate an error.
This call is intended to provide the ability to securely scrub memory
without compiler interference, in a similar manner to explicit_bzero,
memset_s, SecureZeroMemory.
The approach taken is a volatile memset followed by a seqentially
consistent memory fence, to prevent the call from being optimized away
by DSE, and from being reordered. An identical approach is currently
being used by the zeroize Rust crate, and is effective in practice.
LLVM IR output:
```
; Function Attrs: nounwind
define internal i8* @mem.zero_explicit(i8* %0, i64 %1) #0 {
decls:
call void @llvm.memset.p0i8.i64(i8* %0, i8 0, i64 %1, i1 true)
fence seq_cst
ret i8* %0
}
```
Yawning Angel