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-rw-r--r--src/ec25519_gf.c4
1 files changed, 4 insertions, 0 deletions
diff --git a/src/ec25519_gf.c b/src/ec25519_gf.c
index 91fa320..4914fa7 100644
--- a/src/ec25519_gf.c
+++ b/src/ec25519_gf.c
@@ -271,6 +271,10 @@ void ecc_25519_gf_recip(ecc_int256_t *out, const ecc_int256_t *in) {
/**
* Ensures some properties of a Galois field element to make it fit for use as a secret key
*
+ * This sets the 255th bit and clears the 256th and the bottom three bits (so the key
+ * will be a multiple of 8). See Daniel J. Bernsteins paper "Curve25519: new Diffie-Hellman speed records."
+ * for the rationale of this.
+ *
* The same pointers may be used for input and output.
*/
void ecc_25519_gf_sanitize_secret(ecc_int256_t *out, const ecc_int256_t *in) {