di_ops.c File Reference

Functions for data-independent operations. More...

#include "orconfig.h"
#include "di_ops.h"
#include "torlog.h"
#include "util.h"

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Data Structures
struct	di_digest256_map_t

Functions
int	tor_memcmp (const void *a, const void *b, size_t len)
int	tor_memeq (const void *a, const void *b, size_t sz)
void	dimap_free_ (di_digest256_map_t *map, dimap_free_fn free_fn)
void	dimap_add_entry (di_digest256_map_t **map, const uint8_t *key, void *val)
void *	dimap_search (const di_digest256_map_t *map, const uint8_t *key, void *dflt_val)
int	safe_mem_is_zero (const void *mem, size_t sz)
int	select_array_member_cumulative_timei (const uint64_t *entries, int n_entries, uint64_t total, uint64_t rand_val)

Detailed Description

Functions for data-independent operations.

Function Documentation

dimap_add_entry()

void dimap_add_entry	(	di_digest256_map_t **	map,
		const uint8_t *	key,
		void *	val
	)

Adjust the map at *map, adding an entry for key -> val, where key is a DIGEST256_LEN-byte key.

The caller MUST NOT add a key that already appears in the map.

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dimap_free_()

void dimap_free_	(	di_digest256_map_t *	map,
		dimap_free_fn	free_fn
	)

Release all storage held in map, calling free_fn on each value as we go.

dimap_search()

void* dimap_search	(	const di_digest256_map_t *	map,
		const uint8_t *	key,
		void *	dflt_val
	)

Search the map at map for an entry whose key is key (a DIGEST256_LEN-byte key) returning the corresponding value if we found one, and returning dflt_val if the key wasn't found.

This operation takes an amount of time dependent only on the length of map, not on the position or presence of key within map.

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safe_mem_is_zero()

int safe_mem_is_zero	(	const void *	mem,
		size_t	sz
	)

Return true iff the sz bytes at mem are all zero. Runs in time independent of the contents of mem.

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select_array_member_cumulative_timei()

int select_array_member_cumulative_timei	(	const uint64_t *	entries,
		int	n_entries,
		uint64_t	total,
		uint64_t	rand_val
	)

Given an array of list of n_entries uint64_t values, whose sum is total, find the first i such that the total of all elements 0...i is greater than rand_val.

Try to perform this operation in a constant-time way.

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tor_memcmp()

int tor_memcmp	(	const void *	a,
		const void *	b,
		size_t	len
	)

Timing-safe version of memcmp. As memcmp, compare the sz bytes at a with the sz bytes at b, and return less than 0 if the bytes at a lexically precede those at b, 0 if the byte ranges are equal, and greater than zero if the bytes at a lexically follow those at b.

This implementation differs from memcmp in that its timing behavior is not data-dependent: it should return in the same amount of time regardless of the contents of a and b.

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tor_memeq()

int tor_memeq	(	const void *	a,
		const void *	b,
		size_t	sz
	)

Timing-safe memory comparison. Return true if the sz bytes at a are the same as the sz bytes at b, and 0 otherwise.

This implementation differs from !memcmp(a,b,sz) in that its timing behavior is not data-dependent: it should return in the same amount of time regardless of the contents of a and b. It differs from !tor_memcmp(a,b,sz) by being faster.

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