docs(cipher): fix salt misuse resistance calculations [#16]

[rmlibre]

Description

Detailed in (#16)

Expected behavior

Detailed in (#16)

Remediations

Apply documentation updates

• doc strings

There were two different passage types, both of which were updated.

aiootp/aiootp/ciphers/key_bundle.py

Lines 225 to 245 in 0f072eb

	@property
	def salt(self) -> bytes:
	"""
	A [pseudo]random salt that may be supplied by the user. By
	default it's sent in the clear attached to the ciphertext.
	Thus it may simplify implementing efficient features, such
	as search or routing, though care must still be taken when
	considering how leaking such metadata may be harmful.
	Keeping this value constant is strongly discouraged. Though,
	the cipher's salt misuse-reuse resistance is ruled by the
	combination of the automatically incorporated `timestamp`,
	`iv`, & `siv_key`. The risk calculation starts with setting
	r = len(iv + siv_key) / 3. Then, all else staying constant,
	once 256**r messages are encrypted within a second, each
	additional encrypted message within that same second begins
	to have more than a 256**(-r) chance of generating a repeat
	context.
	See: https://github.com/rmlibre/aiootp/issues/16
	"""

aiootp/aiootp/ciphers/padding.py

Lines 58 to 67 in 0f072eb

	`Inner-Header`: Prepends a timestamp & SIV-key. The timestamp supports
	a time-to-live feature for ciphertexts which can mitigate replay
	attacks. Together with the random SIV-key, the uniqueness of the
	session's initialization is ensured on every tick of the clock,
	therefore extending salt misuse-reuse resistance. The risk
	calculation starts with setting r = len(iv + siv_key) / 3. Then,
	all else staying constant, once 256**r messages are encrypted
	within a second, each additional encrypted message within that
	same second begins to have more than a 256**(-r) chance of
	generating a repeat context.

• README.rst

There were no detailed passages specifically mentioning these calculations in the readme.

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Resolution related to (#16)

[rmlibre]

Resolved by (ea07198)