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70 lines
3.5 KiB
Markdown
70 lines
3.5 KiB
Markdown
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# How this package works
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### Chapter 1: [Making private things public](./u_public.go)
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There are numerous handshake-related structs in crypto/tls, most of which are either private or have private fields.
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One of them — `clientHandshakeState` — has private function `handshake()`,
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which is called in the beginning of default handshake.
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Unfortunately, user will not be able to directly access this struct outside of tls package.
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As a result, we decided to employ following workaround: declare public copies of private structs.
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Now user is free to manipulate fields of public `ClientHandshakeState`.
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Then, right before handshake, we can shallow-copy public state into private `clientHandshakeState`,
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call `handshake()` on it and carry on with default Golang handshake process.
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After handshake is done we shallow-copy private state back to public, allowing user to read results of handshake.
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### Chapter 2: [TLSExtension](./u_tls_extensions.go)
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The way we achieve reasonable flexibilty with extensions is inspired by
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[ztls'](https://github.com/zmap/zcrypto/blob/master/tls/handshake_extensions.go) design.
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However, our design has several differences, so we wrote it from scratch.
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This design allows us to have an array of `TLSExtension` objects and then marshal them in order:
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```Golang
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type TLSExtension interface {
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writeToUConn(*UConn) error
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Len() int // includes header
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// Read reads up to len(p) bytes into p.
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// It returns the number of bytes read (0 <= n <= len(p)) and any error encountered.
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Read(p []byte) (n int, err error) // implements io.Reader
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}
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```
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`writeToUConn()` applies appropriate per-extension changes to `UConn`.
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`Len()` provides the size of marshaled extension, so we can allocate appropriate buffer beforehand,
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catch out-of-bound errors easily and guide size-dependent extensions such as padding.
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`Read(buffer []byte)` _writes(see: io.Reader interface)_ marshaled extensions into provided buffer.
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This avoids extra allocations.
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### Chapter 3: [UConn](./u_conn.go)
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`UConn` extends standard `tls.Conn`. Most notably, it stores slice with `TLSExtension`s and public
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`ClientHandshakeState`.
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Whenever `UConn.BuildHandshakeState()` gets called (happens automatically in `UConn.Handshake()`
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or could be called manually), config will be applied according to chosen `ClientHelloID`.
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From contributor's view there are 2 main behaviors:
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* `HelloGolang` simply calls default Golang's [`makeClientHello()`](./handshake_client.go)
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and directly stores it into `HandshakeState.Hello`. utls-specific stuff is ignored.
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* Other ClientHelloIDs fill `UConn.Hello.{Random, CipherSuites, CompressionMethods}` and `UConn.Extensions` with
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per-parrot setup, which then gets applied to appropriate standard tls structs,
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and then marshaled by utls into `HandshakeState.Hello`.
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### Chapter 4: Tests
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Tests exist, but coverage is very limited. What's covered is a conjunction of
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* TLS 1.2
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* Working parrots without any unsupported extensions (only Android 5.1 at this time)
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* Ciphersuites offered by parrot.
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* Ciphersuites supported by Golang
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* Simple conversation with reference implementation of OpenSSL.
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(e.g. no automatic checks for renegotiations, parroting quality and such)
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plus we test some other minor things.
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Basically, current tests aim to provide a sanity check.
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# Merging upstream
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```Bash
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git remote add -f golang git@github.com:golang/go.git
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git checkout -b golang-upstream golang/master
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git subtree split -P src/crypto/tls/ -b golang-tls-upstream
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git checkout master
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git merge --no-commit golang-tls-upstream
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```
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