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Fix ECH payload size varying per-connection instead of per-process #2

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Fix ECH payload size varying per-connection instead of per-process #2

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Copilot Apr 5, 2026
c5ccab2
Fix ECH payload size to be per-connection random for better DPI bypass
Copilot Apr 5, 2026
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22 changes: 19 additions & 3 deletions td/mtproto/TlsInit.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -51,7 +51,8 @@ class TlsHello {
BeginScope,
EndScope,
Permutation,
Padding
Padding,
EchPayload
};
Type type;
int length;
Expand Down Expand Up @@ -116,8 +117,7 @@ class TlsHello {
}
static Op ech_payload() {
Op res;
res.type = Type::Random;
res.length = Random::fast(0, 3) * 32 + 144;
res.type = Type::EchPayload;
return res;
}
static Op padding() {
Expand Down Expand Up @@ -232,6 +232,7 @@ class TlsHelloContext {
public:
TlsHelloContext(size_t grease_size, string domain) : grease_(grease_size, '\0'), domain_(std::move(domain)) {
Grease::init(grease_);
ech_payload_size_ = static_cast<size_t>(Random::fast(0, 3)) * 32 + 144;
}

char get_grease(size_t i) const {
Expand All @@ -244,10 +245,14 @@ class TlsHelloContext {
Slice get_domain() const {
return Slice(domain_).substr(0, ProxySecret::MAX_DOMAIN_LENGTH);
}
size_t get_ech_payload_size() const {
return ech_payload_size_;
}

private:
string grease_;
string domain_;
size_t ech_payload_size_;
};

class TlsHelloCalcLength {
Expand Down Expand Up @@ -320,6 +325,10 @@ class TlsHelloCalcLength {
size_ = 517;
}
break;
case Type::EchPayload:
CHECK(context);
size_ += context->get_ech_payload_size();
break;
default:
UNREACHABLE();
}
Expand Down Expand Up @@ -468,6 +477,13 @@ class TlsHelloStore {
}
break;
}
case Type::EchPayload: {
CHECK(context);
auto payload_size = context->get_ech_payload_size();
Random::secure_bytes(dest_.substr(0, payload_size));
dest_.remove_prefix(payload_size);
break;
}
default:
UNREACHABLE();
}
Expand Down