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TLS Hello Fragmenting: New Single TLS Hello Fragmenting Method #3660

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radioactiveAHM wants to merge 4 commits into from
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TLS Hello Fragmenting: New Single TLS Hello Fragmenting Method #3660

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a6c20ba
add single tls hello fragmenting method
radioactiveAHM Aug 8, 2024
2856413
Rename
Fangliding Aug 9, 2024
7c898f9
Use actual record header version
Fangliding Aug 9, 2024
2cfeef3
Revert
Fangliding Aug 9, 2024
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4 changes: 4 additions & 0 deletions infra/conf/freedom.go
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Original file line number Diff line number Diff line change
Expand Up @@ -62,6 +62,10 @@ func (c *FreedomConfig) Build() (proto.Message, error) {
var err, err2 error

switch strings.ToLower(c.Fragment.Packets) {
case "singletlshello":
// TLS Hello Fragmentation (into multiple handshake messages but one tcp segment)
config.Fragment.PacketsFrom = 1
config.Fragment.PacketsTo = 1
case "tlshello":
// TLS Hello Fragmentation (into multiple handshake messages)
config.Fragment.PacketsFrom = 0
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25 changes: 25 additions & 0 deletions proxy/freedom/freedom.go
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Original file line number Diff line number Diff line change
Expand Up @@ -392,6 +392,31 @@ type FragmentWriter struct {
func (f *FragmentWriter) Write(b []byte) (int, error) {
f.count++

if f.fragment.PacketsFrom == 1 && f.fragment.PacketsTo == 1 && f.count == 1 {
// TLS record layer fragments(for client hello)
// Note: TLS handshake doesn't check record layer, so it can be modified by us.
if f.count != 1 || len(b) <= 5 || b[0] != 22 {
return f.writer.Write(b)
}
recordLen := 5 + ((int(b[3]) << 8) | int(b[4]))
if len(b) < recordLen { // Size not match, maybe already fragmented somehow
return f.writer.Write(b)
}

// Build new fragmented client hello
p2 := b[5 : len(b)/2]
p1 := []byte{b[0], b[1], b[2], byte(len(p2) >> 8), byte(len(p2))}
p4 := b[len(b)/2:]
p3 := []byte{b[0], b[1], b[2], byte(len(p4) >> 8), byte(len(p4))}

// 😐 Concat requires go v1.22
x := append(p1, p2...)
x = append(x, p3...)
x = append(x, p4...)

return f.writer.Write(x)
Comment on lines +412 to +417
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@mmmray mmmray Aug 8, 2024 •
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This feels wrong. has it been tested? You are splitting up the bytestring and then concatenate it again. And then write out the entire packet anyway. Normally they should be sent using individual Write calls, with Sleep inbetween. Take a look at the other fragment settings' code, where a for-loop is used.

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@radioactiveAHM radioactiveAHM Aug 8, 2024

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Yes, I tested and checked using Wireshark, and it works fine. I know it’s unusual, but as long as it works, it is useful. The tlshello fragmenting method generates fragments of a specified length, writes each fragment with one TCP segment, and then sleeps for the specified interval. However, this new method splits the TLS ClientHello into two halves, generates two fragments into one buffer, and sends both fragments using one TCP segment.

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@mmmray mmmray Aug 8, 2024

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oh i misunderstood. I just realized you have some hardcoded bytes in there as well.

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@radioactiveAHM radioactiveAHM Aug 8, 2024

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Yes, I have observed that almost all TLS Client Hello messages start with [22, 3, 1], so I hardcoded this value. I don’t anticipate this causing any bugs, but I can make it dynamic if needed.

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@RPRX RPRX Aug 9, 2024

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话说这里为啥备注需要 Go 1.22？append 不是自古以来就有的吗

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@radioactiveAHM radioactiveAHM Aug 9, 2024

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I need go 1.22 for Concat method. with Concat you can do this

slices.Concat(p1, p2, p3, p4)

}

if f.fragment.PacketsFrom == 0 && f.fragment.PacketsTo == 1 {
if f.count != 1 || len(b) <= 5 || b[0] != 22 {
return f.writer.Write(b)
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