SecretKey::to_bytes shouldn't be unsafe

[sosthene-nitrokey]

unsafe refers to memory safety, not generally "dangerous" APIs. I don't think it should be use for this kind of use cases. For example, neither the secrecy or untrusted use unsafe this way.

To warn against exporting the secret key, I'd recommend removing unsafe and renaming it to subtle_to_bytes or something similar.

[szszszsz]

p256-cortex-m4/src/cortex_m4.rs

Lines 130 to 142 in 290b275

	#[allow(unused_unsafe)]
	/// Convert endianness to obtain the big-endian representation of the secret scalar as 32 bytes.
	///
	/// "unsafe" because the caller is responsible for keeping the value secret.
	pub unsafe fn to_bytes(&self) -> [u8; 32] {
	let mut big_endian = [0u8; 32];
	unsafe { p256_cortex_m4_sys::p256_convert_endianness(
	&mut big_endian[0] as *mut u8 as *mut _,
	&self.0[0] as *const u32 as *const _,
	32,
	) };
	big_endian
	}