mbedtls_ct_memcpy_offset() function

Copy data from a secret position. Functionally equivalent to: memcpy(dst, src + offset, len) This function copies \p len bytes from \p src + \p offset to \p dst, with a code flow and memory access pattern that does not depend on \p offset, but only on \p offset_min, \p offset_max and \p len.

Syntax

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Summary

Declaration

Definition

from constant_time_internal.h:531

void mbedtls_ct_memcpy_offset(unsigned char *dest, const unsigned char *src, size_t offset, size_t offset_min, size_t offset_max, size_t len);

Implemented in constant_time.c:215

Arguments

Argument

Declared as

Description

dest

unsigned char *

Secret. The destination buffer. This must point to a writable buffer of at least \p len bytes.

src

const unsigned char *

Secret. The base of the source buffer. This must point to a readable buffer of at least \p offset_max + \p len bytes. Shouldn't overlap with \p dest

offset

size_t

Secret. The offset in the source buffer from which to copy. This must be no less than \p offset_min and no greater than \p offset_max.

offset_min

size_t

The minimal value of \p offset.

offset_max

size_t

The maximal value of \p offset.

len

size_t

The number of bytes to copy.

Notes

This function reads from \p dest, but the value that is read does not influence the result and this function's behavior is well-defined regardless of the contents of the buffers. This may result in false positives from static or dynamic analyzers, especially if \p dest is not initialized.