moving onwards

ssh.lua

@@ -4,9 +4,6 @@ local program_string = program_name .. "_" .. program_version
 
 local component = require("component")
 local internet = component.internet
-local event = require("event")
-local computer = require("computer")
-local serialize = require("serialize")
 
 local function lazy_require(name)
     local this = {}
@@ -16,15 +13,16 @@ local function lazy_require(name)
             module = module or require(name)
             return module[key]
         end,
-       __call = function(_, ...)
-           module = module or require(name)
-           return module(...)
-       end
+        __call = function(_, ...)
+            module = module or require(name)
+            return module(...)
+        end
     })
     return this
 end
 
-local curve25519 = lazy_require("curve25519")
+local x25519 = lazy_require("x25519")
+local sha2 = lazy_require("sha256")
 
 local function parse_ssh_version(str)
     local proto, software, comments = str:match("^SSH%-(%d+%.%d+)%-(%S+)%s?(.*)\r\n$")
@@ -58,6 +56,79 @@ local SSH_MSG_SERVICE_ACCEPT = 6
 local SSH_MSG_KEXINIT = 20
 local SSH_MSG_NEWKEYS = 21
 
+-- RFC 4253 7.1: first entry in client list that also appears in server_list wins
+local function negotiate_one(client_list, server_list)
+    local server_set = {}
+    for _, name in ipairs(server_list) do server_set[name] = true end
+    for _, name in ipairs(client_list) do
+        if server_set[name] then return name end
+    end
+    return nil
+end
+
+local function negotiate(client_algs, server_kex)
+    local chosen = {}
+    for field, _ in pairs(client_algs) do
+        chosen[field] = negotiate_one(client_algs[field] or {}, server_kex[field] or {})
+        local is_language_field = field:find("^languages_")
+        if not chosen[field] and not is_language_field then
+            return nil, "no agreement on " .. field
+        end
+    end
+    return chosen
+end
+
+local function xor_with_byte(s, b)
+    local out = {}
+    for i = 1, #s do
+        out[i] = string.char(string.byte(s, i) ~ b)
+    end
+    return table.concat(out)
+end
+
+local function hmac(hash_fn, block_size, key, message)
+    if #key > block_size then key = hash_fn(key) end
+    if #key < block_size then key = key .. string.rep('\0', block_size - #key) end
+    return hash_fn(xor_with_byte(key, 0x5c) .. hash_fn(xor_with_byte(key, 0x36) .. message))
+end
+
+local mac_algorithms_priority = {
+    "hmac-sha2-256",
+    "hmac-sha2-512",
+    --"hmac-sha1"
+}
+
+local mac_algorithms = {
+    ["hmac-sha2-256"] = function(key, message) return hmac(sha2.sha256, 64, key, message) end,
+    ["hmac-sha2-512"] = function(key, message) return hmac(sha2.sha512, 128, key, message) end,
+    --["hmac-sha1"] = function(key, message) return hmac(sha1, 64, key, message) end,
+}
+
+local encryption_algorithms_priority = {
+    "chacha20-poly1305@openssh.com",
+-- aes128-gcm@openssh.com
+-- aes256-gcm@openssh.com
+-- aes128-ctr
+-- aes192-ctr
+-- aes256-ctr
+}
+local encryption_algorithms = {
+    ["chacha20-poly1305@openssh.com"] = nil
+}
+
+local server_host_key_algorithms_priority = {
+    --[[
+    "rsa-sha2-512",
+    "rsa-sha2-256",
+    "ecdsa-sha2-nistp256",
+    "ssh-ed25519"
+    ]]
+}
+
+local server_host_key_algorithms = {
+
+}
+
 local function socket()
     local this = {}
     local _sock
@@ -89,7 +160,11 @@ local function socket()
         while #_read_buf < n do
             local chunk, err = _sock.read(n - #_read_buf)
             if chunk == nil then return nil, err end
-            _read_buf = _read_buf .. chunk
+            if chunk == "" then
+                coroutine.yield()
+            else
+                _read_buf = _read_buf .. chunk
+            end
         end
         local to_return = _read_buf:sub(1, n);
         _read_buf = _read_buf:sub(n + 1, -1)
@@ -239,26 +314,47 @@ end
 local sock = socket()
 sock.connect("localhost", 22)
 -- RFC 4253: The maximum length of the string is 255 characters
-local server_protoversion, server_softwareversion, server_comments = parse_ssh_version(sock.read_until_crlf(255))
+local server_version_raw = sock.read_until_crlf(255)
+local server_protoversion, server_softwareversion, server_comments = parse_ssh_version(server_version_raw)
 if server_protoversion ~= "2.0" then
     return
 end
-sock.write(encode_ssh_version("2.0", program_string))
-print(sock.parse_kexinit(sock.read_packet()))
---[[
+
+local client_version_line = encode_ssh_version("2.0", program_string)
+sock.write(client_version_line)
+
+local V_C = client_version_line:gsub("\r\n$", "")
+local V_S = server_version_raw:gsub("\r\n$", "")
+
+local I_S, kerr = sock.read_packet()
+if not I_S then
+    print("failed to read server KEXINIT: " .. tostring(kerr))
+    return
+end
+local server_kex, perr = sock.parse_kexinit(I_S)
+if not server_kex then
+    print("failed to parse server KEXINIT: " .. tostring(perr))
+    return
+end
+
 local my_algs = {
-    kex_algorithms = {},
-    server_host_key_algorithms = {},
-    encryption_algorithms_client_to_server = {},
-    encryption_algorithms_server_to_client = {},
-    mac_algorithms_client_to_server = {},
-    mac_algorithms_server_to_client = {},
+    kex_algorithms = { "curve25519-sha256" },
+    server_host_key_algorithms = server_host_key_algorithms,
+    encryption_algorithms_client_to_server = encryption_algorithms_priority,
+    encryption_algorithms_server_to_client = encryption_algorithms_priority,
+    mac_algorithms_client_to_server = mac_algorithms_priority,
+    mac_algorithms_server_to_client = mac_algorithms_priority,
     compression_algorithms_client_to_server = { "none" },
     compression_algorithms_server_to_client = { "none" },
     languages_client_to_server = {},
     languages_server_to_client = {},
 }
 
-local my_kexinit_payload = sock.build_kexinit(my_algs)
-sock.write_packet(my_kexinit_payload)
-]]
+local I_C = sock.build_kexinit(my_algs)
+sock.write_packet(I_C)
+
+local chosen, nerr = negotiate(my_algs, server_kex)
+if not chosen then
+    print("algorithm negotiation failed: " .. tostring(nerr))
+    return
+end