From 02437dc60ede06ce115c8a849316b82087f88e87 Mon Sep 17 00:00:00 2001 From: akwizgran Date: Sat, 11 Apr 2015 16:28:56 +0000 Subject: [PATCH] akwizgran created page: BQP --- BTP.markdown | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/BTP.markdown b/BTP.markdown index 11c2337..7403778 100644 --- a/BTP.markdown +++ b/BTP.markdown @@ -15,6 +15,10 @@ BTP uses the following cryptographic primitives: * A message authentication code, MAC(k, m) * An authenticated cipher, ENC(k, n, m) and DEC(k, n, m), where n is a nonce +We use MAC(k, m) to define a key derivation function: + +* `KDF(k, x_1, ..., x_n) == MAC(k, len(x_1) || x_1 || ... || len(x_n) || x_n)` + All keys are KEY_LEN bytes and all nonces are NONCE_LEN bytes. The output of MAC(k, m) is MAC_LEN bytes, and the output of ENC(k, n, m) is AUTH_LEN bytes longer than m. For simplicity we require that MAC_LEN == KEY_LEN. > Implementation note: The current implementation uses HMAC-SHA-256 as the message authentication code and AES-256-GCM as the authenticated cipher. In the next release we propose to use keyed BLAKE2s as the message authentication code and XSalsa20/Poly1305 as the authenticated cipher. This gives KEY_LEN = 32, MAC_LEN = 32, NONCE_LEN = 24, and AUTH_LEN = 16. @@ -36,10 +40,6 @@ The devices must also agree which of them will play the role of Alice and which ### Key derivation -BTP's key derivation function is based on a message authentication code: - -* `KDF(k, x_1, ..., x_n) == MAC(k, len(x_1) || x_1 || ... || len(x_n) || x_n)` - Each device derives four initial keys from S: * `atk = KDF(S, "ALICE_TAG_KEY")`