1 files changed, 36 insertions, 0 deletions
diff --git a/include/mbedtls/constant_time.h b/include/mbedtls/constant_time.h
new file mode 100644
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--- /dev/null
+++ b/include/mbedtls/constant_time.h
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+/**
+ *  Constant-time functions
+ */
+/*
+ *  Copyright The Mbed TLS Contributors
+ *  SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later
+ */
+
+#ifndef MBEDTLS_CONSTANT_TIME_H
+#define MBEDTLS_CONSTANT_TIME_H
+
+#include <stddef.h>
+
+/** Constant-time buffer comparison without branches.
+ *
+ * This is equivalent to the standard memcmp function, but is likely to be
+ * compiled to code using bitwise operations rather than a branch, such that
+ * the time taken is constant w.r.t. the data pointed to by \p a and \p b,
+ * and w.r.t. whether \p a and \p b are equal or not. It is not constant-time
+ * w.r.t. \p n .
+ *
+ * This function can be used to write constant-time code by replacing branches
+ * with bit operations using masks.
+ *
+ * \param a     Pointer to the first buffer, containing at least \p n bytes. May not be NULL.
+ * \param b     Pointer to the second buffer, containing at least \p n bytes. May not be NULL.
+ * \param n     The number of bytes to compare.
+ *
+ * \return      Zero if the contents of the two buffers are the same,
+ *              otherwise non-zero.
+ */
+int mbedtls_ct_memcmp(const void *a,
+                      const void *b,
+                      size_t n);
+
+#endif /* MBEDTLS_CONSTANT_TIME_H */