subtle package - crypto/subtle - Go Packages (original) (raw)

Package subtle implements functions that are often useful in cryptographic code but require careful thought to use correctly.

func ConstantTimeByteEq(x, y uint8) int
func ConstantTimeCompare(x, y []byte) int
func ConstantTimeCopy(v int, x, y []byte)
func ConstantTimeEq(x, y int32) int
func ConstantTimeLessOrEq(x, y int) int
func ConstantTimeSelect(v, x, y int) int
func WithDataIndependentTiming(f func())
func XORBytes(dst, x, y []byte) int

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ConstantTimeByteEq returns 1 if x == y and 0 otherwise.

func ConstantTimeCompare(x, y []byte) int

ConstantTimeCompare returns 1 if the two slices, x and y, have equal contents and 0 otherwise. The time taken is a function of the length of the slices and is independent of the contents. If the lengths of x and y do not match it returns 0 immediately.

func ConstantTimeCopy(v int, x, y []byte)

ConstantTimeCopy copies the contents of y into x (a slice of equal length) if v == 1. If v == 0, x is left unchanged. Its behavior is undefined if v takes any other value.

ConstantTimeEq returns 1 if x == y and 0 otherwise.

func ConstantTimeLessOrEq(x, y int) int

ConstantTimeLessOrEq returns 1 if x <= y and 0 otherwise. Its behavior is undefined if x or y are negative or > 2**31 - 1.

func ConstantTimeSelect(v, x, y int) int

ConstantTimeSelect returns x if v == 1 and y if v == 0. Its behavior is undefined if v takes any other value.

func WithDataIndependentTiming(f func())

WithDataIndependentTiming enables architecture specific features which ensure that the timing of specific instructions is independent of their inputs before executing f. On f returning it disables these features.

WithDataIndependentTiming should only be used when f is written to make use of constant-time operations. WithDataIndependentTiming does not make variable-time code constant-time.

WithDataIndependentTiming may lock the current goroutine to the OS thread for the duration of f. Calls to WithDataIndependentTiming may be nested.

On Arm64 processors with FEAT_DIT, WithDataIndependentTiming enables PSTATE.DIT. See https://developer.arm.com/documentation/ka005181/1-0/?lang=en.

Currently, on all other architectures WithDataIndependentTiming executes f immediately with no other side-effects.

func XORBytes(dst, x, y []byte) int

XORBytes sets dst[i] = x[i] ^ y[i] for all i < n = min(len(x), len(y)), returning n, the number of bytes written to dst.

If dst does not have length at least n, XORBytes panics without writing anything to dst.

dst and x or y may overlap exactly or not at all, otherwise XORBytes may panic.

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