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%% Steps for S2S Dialback. |
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%% Diagram from https://xmpp.org/extensions/xep-0220.html#intro-howitworks |
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%% |
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%% Initiating Receiving |
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%% Server Server |
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%% ----------- --------- |
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%% | | |
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%% | [if necessary, | |
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%% | perform DNS lookup | |
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%% | on Target Domain, | |
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%% | open TCP connection, | |
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%% | and establish stream] | |
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%% | -----------------------> | |
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%% | | Authoritative |
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%% | send dialback key | Server |
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%% | -------(STEP 1)--------> | ------------- |
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%% | | | |
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%% | | [if necessary, | |
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%% | | perform DNS lookup, | |
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%% | | on Sender Domain, | |
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%% | | open TCP connection, | |
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%% | | and establish stream] | |
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%% | | -----------------------> | |
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%% | | | |
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%% | | send verify request | |
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%% | | -------(STEP 2)--------> | |
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%% | | | |
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%% | | send verify response | |
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%% | | <------(STEP 3)--------- | |
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%% | | |
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%% | report dialback result | |
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%% | <-------(STEP 4)-------- | |
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%% | | |
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%% Because db:result and db:verify tags are confusing, use step numbers. |
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%% (db:result should've been named db:key). |
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-module(mongoose_s2s_dialback). |
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-export([step_1/2, |
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step_2/3, |
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step_3/3, |
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step_4/2]). |
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-export([parse_key/1, |
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parse_validity/1]). |
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-export([make_key/3]). |
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-xep([{xep, 185}, {version, "1.0"}]). %% Dialback Key Generation and Validation |
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-xep([{xep, 220}, {version, "1.1.1"}]). %% Server Dialback |
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-include("mongoose.hrl"). |
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-include("jlib.hrl"). |
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%% Initiating server sends dialback key |
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%% https://xmpp.org/extensions/xep-0220.html#example-1 |
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-spec step_1(ejabberd_s2s:fromto(), ejabberd_s2s:s2s_dialback_key()) -> exml:element(). |
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step_1(FromTo, Key) -> |
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:-( |
#xmlel{name = <<"db:result">>, |
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attrs = fromto_to_attrs(FromTo), |
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children = [#xmlcdata{content = Key}]}. |
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%% Receiving server sends verification request to authoritative server (step 2) |
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-spec step_2(ejabberd_s2s:fromto(), ejabberd_s2s:s2s_dialback_key(), ejabberd_s2s:stream_id()) -> exml:element(). |
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step_2(FromTo, Key, StreamID) -> |
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:-( |
#xmlel{name = <<"db:verify">>, |
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attrs = [{<<"id">>, StreamID} | fromto_to_attrs(FromTo)], |
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children = [#xmlcdata{content = Key}]}. |
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%% Receiving server is informed by authoritative server that key is valid or invalid (step 3) |
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-spec step_3(ejabberd_s2s:fromto(), ejabberd_s2s:stream_id(), boolean()) -> exml:element(). |
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step_3(FromTo, StreamID, IsValid) -> |
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:-( |
#xmlel{name = <<"db:verify">>, |
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attrs = [{<<"id">>, StreamID}, |
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{<<"type">>, is_valid_to_type(IsValid)} |
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| fromto_to_attrs(FromTo)]}. |
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%% Receiving server sends valid or invalid verification result to initiating server (step 4) |
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-spec step_4(ejabberd_s2s:fromto(), boolean()) -> exml:element(). |
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step_4(FromTo, IsValid) -> |
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#xmlel{name = <<"db:result">>, |
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attrs = [{<<"type">>, is_valid_to_type(IsValid)} |
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| fromto_to_attrs(FromTo)]}. |
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-spec fromto_to_attrs(ejabberd_s2s:fromto()) -> [{binary(), binary()}]. |
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fromto_to_attrs({LocalServer, RemoteServer}) -> |
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:-( |
[{<<"from">>, LocalServer}, {<<"to">>, RemoteServer}]. |
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is_valid_to_type(true) -> <<"valid">>; |
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:-( |
is_valid_to_type(false) -> <<"invalid">>. |
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-spec parse_key(exml:element()) -> false |
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| {Step :: step_1 | step_2, |
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FromTo :: ejabberd_s2s:fromto(), |
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StreamID :: ejabberd_s2s:stream_id(), |
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Key :: ejabberd_s2s:s2s_dialback_key()}. |
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parse_key(El = #xmlel{name = <<"db:result">>}) -> |
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%% Initiating Server Sends Dialback Key (Step 1) |
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:-( |
parse_key(step_1, El); |
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parse_key(El = #xmlel{name = <<"db:verify">>}) -> |
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%% Receiving Server Sends Verification Request to Authoritative Server (Step 2) |
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:-( |
parse_key(step_2, El); |
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parse_key(_) -> |
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:-( |
false. |
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parse_key(Step, El) -> |
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:-( |
FromTo = parse_from_to(El), |
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:-( |
StreamID = exml_query:attr(El, <<"id">>, <<>>), |
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:-( |
Key = exml_query:cdata(El), |
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{Step, FromTo, StreamID, Key}. |
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%% Parse dialback verification result. |
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%% Verification result is stored in the `type' attribute and could be `valid' or `invalid'. |
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-spec parse_validity(exml:element()) -> false |
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| {Step :: step_3 | step_4, |
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FromTo :: ejabberd_s2s:fromto(), |
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StreamID :: ejabberd_s2s:stream_id(), |
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IsValid :: boolean()}. |
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parse_validity(El = #xmlel{name = <<"db:verify">>}) -> |
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%% Receiving Server is Informed by Authoritative Server that Key is Valid or Invalid (Step 3) |
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:-( |
parse_validity(step_3, El); |
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parse_validity(El = #xmlel{name = <<"db:result">>}) -> |
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%% Receiving Server Sends Valid or Invalid Verification Result to Initiating Server (Step 4) |
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:-( |
parse_validity(step_4, El); |
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parse_validity(_) -> |
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:-( |
false. |
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parse_validity(Step, El) -> |
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:-( |
FromTo = parse_from_to(El), |
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StreamID = exml_query:attr(El, <<"id">>, <<>>), |
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IsValid = exml_query:attr(El, <<"type">>) =:= <<"valid">>, |
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{Step, FromTo, StreamID, IsValid}. |
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-spec parse_from_to(exml:element()) -> ejabberd_s2s:fromto(). |
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parse_from_to(El) -> |
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:-( |
RemoteJid = jid:from_binary(exml_query:attr(El, <<"from">>, <<>>)), |
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:-( |
LocalJid = jid:from_binary(exml_query:attr(El, <<"to">>, <<>>)), |
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#jid{luser = <<>>, lresource = <<>>, lserver = LRemoteServer} = RemoteJid, |
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#jid{luser = <<>>, lresource = <<>>, lserver = LLocalServer} = LocalJid, |
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%% We use fromto() as seen by ejabberd_s2s_out and ejabberd_s2s |
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:-( |
{LLocalServer, LRemoteServer}. |
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-spec make_key(ejabberd_s2s:fromto(), ejabberd_s2s:stream_id(), ejabberd_s2s:base16_secret()) -> |
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ejabberd_s2s:s2s_dialback_key(). |
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make_key({From, To}, StreamID, Secret) -> |
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:-( |
SecretHashed = base16:encode(crypto:hash(sha256, Secret)), |
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:-( |
HMac = crypto:mac(hmac, sha256, SecretHashed, [From, " ", To, " ", StreamID]), |
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:-( |
base16:encode(HMac). |