Re: [tor-bugs] #17556 [Tor]: Doc or implementation error in NTor handshake

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#17556: Doc or implementation error in NTor handshake
--------------------+---------------------------
 Reporter:  awick   |          Owner:
     Type:  defect  |         Status:  closed
 Priority:  Medium  |      Milestone:
Component:  Tor     |        Version:
 Severity:  Normal  |     Resolution:  not a bug
 Keywords:          |  Actual Points:
Parent ID:          |         Points:
  Sponsor:          |
--------------------+---------------------------
Changes (by yawning):

 * status:  reopened => closed
 * resolution:   => not a bug


Comment:

 Both of the calls to HKDF-SHA256 look like this:
 {{{
   crypto_expand_key_material_rfc5869_sha256(
                            s.secret_input, sizeof(s.secret_input),
                            (const uint8_t*)T->t_key, strlen(T->t_key),
                            (const uint8_t*)T->m_expand,
 strlen(T->m_expand),
                            key_out, key_out_len);
 }}}

 The relevant portions of the function being called looks like this:
 {{{
 int
 crypto_expand_key_material_rfc5869_sha256(
                                     const uint8_t *key_in, size_t
 key_in_len,
                                     const uint8_t *salt_in, size_t
 salt_in_len,
                                     const uint8_t *info_in, size_t
 info_in_len,
                                     uint8_t *key_out, size_t key_out_len)
 {
   // Blah blah blah.

   crypto_hmac_sha256((char*)prk,
                      (const char*)salt_in, salt_in_len,
                      (const char*)key_in, key_in_len);
 }}}

 `salt_in` is the tweak (`T->t_key`), `key_in` is the
 secret(`s.secret_input`), so despite your insistence to the contrary, this
 is `crypto_hmac_sha256(prk, T->t_key, s.secret_input)`.

 Still not a bug.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/17556#comment:3>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
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