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clarify length of NTCP message 3

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zzz
2014-11-25 14:20:38 +00:00
parent 528f105123
commit cfb22c84b7
1 changed files with 11 additions and 2 deletions
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i2p2www/pages/site/docs/transport/ntcp.html
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@ -1,7 +1,7 @@
{% extends "global/layout.html" %} {% extends "global/layout.html" %}
{% block title %}{% trans %}NTCP (NIO-based TCP){% endtrans %}{% endblock %} {% block title %}{% trans %}NTCP (NIO-based TCP){% endtrans %}{% endblock %}
{% block lastupdated %}{% trans %}October 2014{% endtrans %}{% endblock %} {% block lastupdated %}{% trans %}November 2014{% endtrans %}{% endblock %}
{% block accuratefor %}0.9.15{% endblock %} {% block accuratefor %}0.9.17{% endblock %}
{% block content %} {% block content %}
<p>{% trans transports=site_url('docs/transport'), ssu=site_url('docs/transport/ssu') -%} <p>{% trans transports=site_url('docs/transport'), ssu=site_url('docs/transport/ssu') -%}
NTCP is one of two <a href="{{ transports }}">transports</a> currently implemented in I2P. NTCP is one of two <a href="{{ transports }}">transports</a> currently implemented in I2P.
@ -390,6 +390,7 @@ the `Signature` of the following concatenated data:
448 bytes <a href="{{ cryptography }}#AES">AES encrypted</a> using the DH session key and 448 bytes <a href="{{ cryptography }}#AES">AES encrypted</a> using the DH session key and
the last 16 bytes of HXxorHI (i.e., the last 16 bytes of message #1) as the IV the last 16 bytes of HXxorHI (i.e., the last 16 bytes of message #1) as the IV
{%- endtrans %} {%- endtrans %}
448 is the typical length, but it could be longer, see below.
</pre> </pre>
@ -413,6 +414,14 @@ As of release 0.9.16, the router identity may be longer than 387 bytes, and the
are implied by the type of the <a href="{{ site_url('docs/spec/common-structures') }}#type_SigningPublicKey">Signing Public Key</a> are implied by the type of the <a href="{{ site_url('docs/spec/common-structures') }}#type_SigningPublicKey">Signing Public Key</a>
in Alice's <a href="{{ site_url('docs/spec/common-structures') }}#struct_RouterIdentity">Router Identity</a>. in Alice's <a href="{{ site_url('docs/spec/common-structures') }}#struct_RouterIdentity">Router Identity</a>.
The padding is as necessary to a multiple of 16 bytes for the entire unencrypted contents. The padding is as necessary to a multiple of 16 bytes for the entire unencrypted contents.
</li><li>
The total length of the message cannot be determined without partially decrypting it to read the Router Identity.
As the minimum length of the Router Identity is 387 bytes, and the minimum Signature length is 40 (for DSA),
the minimum total message size is 2 + 387 + 4 + (signature length) + (padding to 16 bytes),
or 2 + 387 + 4 + 40 + 15 = 448 for DSA.
The receiver could read that minimum amount before decrypting to determine the actual Router Identity length.
For small Certificates in the Router Identity, that will probably be the entire message, and
there will not be any more bytes in the message to require an additional decryption operation.
</li> </li>
</ul> </ul>