From b9771dae613fa7094ab01c05faedde5e391b2d94 Mon Sep 17 00:00:00 2001 From: Richard van der Hoff Date: Mon, 23 Nov 2020 18:31:08 +0000 Subject: [PATCH] DH ratchet sequence diagram --- docs/DH ratchet.svg | 1 + docs/DH ratchet.txt | 39 +++++++++++++++++++++++++++++++++++++++ 2 files changed, 40 insertions(+) create mode 100644 docs/DH ratchet.svg create mode 100644 docs/DH ratchet.txt diff --git a/docs/DH ratchet.svg b/docs/DH ratchet.svg new file mode 100644 index 0000000..b8f7f0d --- /dev/null +++ b/docs/DH ratchet.svg @@ -0,0 +1 @@ + Alice Bob R[0] = HKDF(0, S)R[0] = HKDF(0, S)generate new ratchet keypair T[0]R[0](msg0), T[0]R[0](msg1), T[0]R[0](msg2), T[0]generate new ratchet keypair T[1]R[1] = HKDF(R[0], DH(T[1], T[0]))R[1](msg3), T[1]R[1] = HKDF(R[0], DH(T[0], T[1]))R[1](msg4), T[1]R[1](msg5), T[1]generate new ratchet keypair T[2]R[2] = HKDF(R[1], DH(T[2], T[1]))R[2](msg6), T[2]R[2] = HKDF(R[1], DH(T[1], T[2]))where:  S is the shared secret derived from the 3ECDH exchange  R[n] is a root key  T[n] is a ratchet keypair  HKDF(salt, key) means performing an HMAC-based key derivation with a salt value of salt and input key material of key  DH(k1, k2) means performing Diffie-Hellman with the private half of k1 and the public half of k2  R[n](msg) means a message encrypted with a key derived from root key R[n] \ No newline at end of file diff --git a/docs/DH ratchet.txt b/docs/DH ratchet.txt new file mode 100644 index 0000000..b52e983 --- /dev/null +++ b/docs/DH ratchet.txt @@ -0,0 +1,39 @@ +lifelinestyle ::solid +participantspacing 10 + +participant :0 " " as p0 +lifelinestyle p0 #white + +actor "Alice" as A + +participant :0 " " as p1 +lifelinestyle p1 #white + +actor "Bob" as B + +participant :0 " " as p2 +lifelinestyle p2 #white + + +parallel +box over A: ""//R[0]//"" = ""HKDF(0, //S//)"" +box over B: ""//R[0]//"" = ""HKDF(0, //S//)"" +parallel off + +box over A: generate new ratchet keypair ""//T[0]//"" +A->B: ""//R[0]//(//msg0//)"", ""//T[0]//"" +A->B: ""//R[0]//(//msg1//)"", ""//T[0]//"" +A->B: ""//R[0]//(//msg2//)"", ""//T[0]//"" +box over B: generate new ratchet keypair ""//T[1]//"" +box over B: ""//R[1]//"" = ""HKDF(//R[0]//, DH(//T[1]//, //T[0]//))"" +B->A: ""//R[1]//(//msg3//)"", ""//T[1]//"" +box over A: ""//R[1]//"" = ""HKDF(//R[0]//, DH(//T[0]//, //T[1]//))"" +B->A: ""//R[1]//(//msg4//)"", ""//T[1]//"" +B->(13)A: ""//R[1]//(//msg5//)"", ""//T[1]//"" +space -14 +box over A: generate new ratchet keypair ""//T[2]//"" +box over A: ""//R[2]//"" = ""HKDF(//R[1]//, DH(//T[2]//, //T[1]//))"" +A->(3)B: ""//R[2]//(//msg6//)"", ""//T[2]//"" +box over B: ""//R[2]//"" = ""HKDF(//R[1]//, DH(//T[1]//, //T[2]//))"" + +box over p0,p2 #EDF2AE:where:\n ""//S//"" is the shared secret derived from the 3ECDH exchange\n ""//R[n]//"" is a root key\n ""//T[n]//"" is a ratchet keypair\n ""HKDF(//salt//, //key//)"" means performing an HMAC-based key derivation with a salt value of ""//salt//"" and input key material of ""//key//""\n ""DH(//k1//, //k2//)"" means performing Diffie-Hellman with the private half of ""//k1//"" and the public half of ""//k2//""\n ""//R[n]//(//msg//)"" means a message encrypted with a key derived from root key ""//R[n]//"" \ No newline at end of file