Support non-zero lowest frame offset

The lowest offset of CRYPTO frames in a QUIC packet does not necessarily start at zero, such as the second packet of a connection using Kyber key in the client hello. Also updates clienthellod to new repo.
refraction-networking · Nov 22, 2024 · cc7f02d · cc7f02d
1 parent cb2c7f1
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diff --git a/README.md b/README.md
@@ -3,8 +3,10 @@
 [![Go Build Status](https://github.com/refraction-networking/uquic/actions/workflows/go_build.yml/badge.svg?branch=master)](https://github.com/refraction-networking/uquic/actions/workflows/go_build.yml)
 [![Ginkgo Test Status](https://github.com/refraction-networking/uquic/actions/workflows/ginkgo_test.yml/badge.svg?branch=master)](https://github.com/refraction-networking/uquic/actions/workflows/ginkgo_test.yml)
 [![godoc](https://img.shields.io/badge/godoc-reference-blue.svg)](https://godoc.org/github.com/refraction-networking/uquic)
+
 ---
-uQUIC is a fork of [quic-go](https://github.com/quic-go/quic-go), which provides Initial Packet fingerprinting resistance and other features. While the handshake is still performed by quic-go, this library provides interface to customize the unencrypted Initial Packet which may reveal fingerprint-able information. 
+
+uQUIC is a fork of [quic-go](https://github.com/quic-go/quic-go), which provides Initial Packet fingerprinting resistance and other features. While the handshake is still performed by quic-go, this library provides interface to customize the unencrypted Initial Packet which may reveal fingerprint-able information.
 
 Golang 1.20+ is required.
 
@@ -13,43 +15,50 @@ If you have any questions, bug reports or contributions, you are welcome to publ
 Development is still in progress and we welcome any contributions adding new features or fixing extant bugs.
 
 # Disclaimer
-This repository belongs to a large research project on how to fingerprint QUIC clients and how to mitigate such fingerprinting. We do not encourage any malicious use of this project's output, including this repository, [uTLS](https://github.com/refraction-networking/utls), and [clienthellod](https://github.com/gaukas/clienthellod).
 
-Our research paper is still yet to be published and therefore this repository is neither ready for production use nor peer-reviewed. And the scope of our research is limited that such mimicry backed by this library MAY NOT be realisticly indistinguishable from the real QUIC clients being mimicked, and some misuses of this library MAY lead to easier fingerprinting against the mimic. We welcome any contributions to improve the realism of the mimicry, as well as expanding the scope of this project. 
+This repository belongs to a large research project on how to fingerprint QUIC clients and how to mitigate such fingerprinting. We do not encourage any malicious use of this project's output, including this repository, [uTLS](https://github.com/refraction-networking/utls), and [clienthellod](https://github.com/refraction-networking/clienthellod).
+
+Our research paper is still yet to be published and therefore this repository is neither ready for production use nor peer-reviewed. And the scope of our research is limited that such mimicry backed by this library MAY NOT be realisticly indistinguishable from the real QUIC clients being mimicked, and some misuses of this library MAY lead to easier fingerprinting against the mimic. We welcome any contributions to improve the realism of the mimicry, as well as expanding the scope of this project.
 
-For anyone intending to use this library for censorship circumvention, please be sure to understand the risks and limitations of this library. 
+For anyone intending to use this library for censorship circumvention, please be sure to understand the risks and limitations of this library.
 
 If you are interested in our research, please stay tuned for our paper.
 
 # Development in Progress
+
 ## Development Roadmap
-- [ ] Customize Initial Packet 
-	- [x] QUIC Header 
-	- [x] QUIC Frame (~~[#3](https://github.com/refraction-networking/uquic/issues/3)~~)
-		- [x] QUIC Crypto Frame
-		- [x] QUIC Padding Frame
-		- [x] QUIC Ping Frame
-		- [ ] QUIC ACK Frame (on hold)
-	- [x] TLS ClientHello Message (by [uTLS](https://github.com/refraction-networking/utls))
-		- [x] QUIC Transport Parameters (in a uTLS extension)
+
+- [ ] Customize Initial Packet
+  - [x] QUIC Header
+  - [x] QUIC Frame (~~[#3](https://github.com/refraction-networking/uquic/issues/3)~~)
+    - [x] QUIC Crypto Frame
+    - [x] QUIC Padding Frame
+    - [x] QUIC Ping Frame
+    - [ ] QUIC ACK Frame (on hold)
+  - [x] TLS ClientHello Message (by [uTLS](https://github.com/refraction-networking/utls))
+    - [x] QUIC Transport Parameters (in a uTLS extension)
 - [ ] Customize Initial ACK behavior ([#1](https://github.com/refraction-networking/uquic/issues/1), [quic-go#4007](https://github.com/quic-go/quic-go/issues/4007))
 - [ ] Customize Initial Retry behavior ([#2](https://github.com/refraction-networking/uquic/issues/2))
 - [ ] Add preset QUIC parrots
-	- [x] Google Chrome parrot (call for parrots w/ `Token/PSK`)
-	- [x] Mozilla Firefox parrot (call for parrots w/ `Token/PSK`)
-	- [ ] Apple Safari parrot
-	- [ ] Microsoft Edge parrot
+  - [x] Google Chrome parrot (call for parrots w/ `Token/PSK`)
+  - [x] Mozilla Firefox parrot (call for parrots w/ `Token/PSK`)
+  - [ ] Apple Safari parrot
+  - [ ] Microsoft Edge parrot
 
 # Features
+
 ## Initial Packet fingerprinting resistance
+
 uQUIC provides a mechanism to customize the Initial Packet, which is unencrypted and is almost unique to every QUIC client implementation. We provide an interface to customize the Initial Packet and makes the fingerprinting of QUIC clients harder.
 
 ### Build a QUIC Spec
-A QUIC Spec sets parameters and policies for uQUIC in establishing a QUIC connection. 
+
+A QUIC Spec sets parameters and policies for uQUIC in establishing a QUIC connection.
 
 See `u_parrot.go` for examples of building a QUIC Spec (parrot).
 
 ### Use a preset QUIC Spec
+
 We provide a few preset QUIC Specs (parrots) for popular QUIC clients in `u_parrot.go`.
 
 To use one, simple invoke `QUICID2Spec(id)`. See below for a complete example of using a preset QUIC Spec in an HTTP3 client.

diff --git a/go.mod b/go.mod
@@ -1,36 +1,35 @@
 module github.com/refraction-networking/uquic
 
-go 1.21
+go 1.21.0
 
 require (
 	github.com/francoispqt/gojay v1.2.13
-	github.com/gaukas/clienthellod v0.4.2
 	github.com/onsi/ginkgo/v2 v2.17.2
 	github.com/onsi/gomega v1.33.1
 	github.com/quic-go/qpack v0.4.0
+	github.com/refraction-networking/clienthellod v0.5.0-alpha2
 	github.com/refraction-networking/utls v1.6.6
 	go.uber.org/mock v0.4.0
-	golang.org/x/crypto v0.22.0
-	golang.org/x/exp v0.0.0-20240416160154-fe59bbe5cc7f
-	golang.org/x/net v0.24.0
+	golang.org/x/crypto v0.23.0
+	golang.org/x/exp v0.0.0-20240506185415-9bf2ced13842
+	golang.org/x/net v0.25.0
 	golang.org/x/sync v0.7.0
-	golang.org/x/sys v0.19.0
+	golang.org/x/sys v0.20.0
 	golang.org/x/time v0.5.0
 )
 
 require (
 	github.com/andybalholm/brotli v1.1.0 // indirect
 	github.com/cloudflare/circl v1.3.8 // indirect
-	github.com/gaukas/godicttls v0.0.4 // indirect
 	github.com/go-logr/logr v1.4.1 // indirect
 	github.com/go-task/slim-sprig/v3 v3.0.0 // indirect
 	github.com/google/go-cmp v0.6.0 // indirect
 	github.com/google/gopacket v1.1.19 // indirect
 	github.com/google/pprof v0.0.0-20240430035430-e4905b036c4e // indirect
 	github.com/klauspost/compress v1.17.8 // indirect
 	golang.org/x/mod v0.17.0 // indirect
-	golang.org/x/text v0.14.0 // indirect
-	golang.org/x/tools v0.20.0 // indirect
+	golang.org/x/text v0.15.0 // indirect
+	golang.org/x/tools v0.21.0 // indirect
 	gopkg.in/check.v1 v1.0.0-20201130134442-10cb98267c6c // indirect
 	gopkg.in/yaml.v3 v3.0.1 // indirect
 )
diff --git a/go.sum b/go.sum
@@ -25,10 +25,6 @@ github.com/flynn/go-shlex v0.0.0-20150515145356-3f9db97f8568/go.mod h1:xEzjJPgXI
 github.com/francoispqt/gojay v1.2.13 h1:d2m3sFjloqoIUQU3TsHBgj6qg/BVGlTBeHDUmyJnXKk=
 github.com/francoispqt/gojay v1.2.13/go.mod h1:ehT5mTG4ua4581f1++1WLG0vPdaA9HaiDsoyrBGkyDY=
 github.com/fsnotify/fsnotify v1.4.7/go.mod h1:jwhsz4b93w/PPRr/qN1Yymfu8t87LnFCMoQvtojpjFo=
-github.com/gaukas/clienthellod v0.4.2 h1:LPJ+LSeqt99pqeCV4C0cllk+pyWmERisP7w6qWr7eqE=
-github.com/gaukas/clienthellod v0.4.2/go.mod h1:M57+dsu0ZScvmdnNxaxsDPM46WhSEdPYAOdNgfL7IKA=
-github.com/gaukas/godicttls v0.0.4 h1:NlRaXb3J6hAnTmWdsEKb9bcSBD6BvcIjdGdeb0zfXbk=
-github.com/gaukas/godicttls v0.0.4/go.mod h1:l6EenT4TLWgTdwslVb4sEMOCf7Bv0JAK67deKr9/NCI=
 github.com/ghodss/yaml v1.0.0/go.mod h1:4dBDuWmgqj2HViK6kFavaiC9ZROes6MMH2rRYeMEF04=
 github.com/gliderlabs/ssh v0.1.1/go.mod h1:U7qILu1NlMHj9FlMhZLlkCdDnU1DBEAqr0aevW3Awn0=
 github.com/go-errors/errors v1.0.1/go.mod h1:f4zRHt4oKfwPJE5k8C9vpYG+aDHdBFUsgrm6/TyX73Q=
@@ -95,6 +91,8 @@ github.com/prometheus/common v0.0.0-20180801064454-c7de2306084e/go.mod h1:daVV7q
 github.com/prometheus/procfs v0.0.0-20180725123919-05ee40e3a273/go.mod h1:c3At6R/oaqEKCNdg8wHV1ftS6bRYblBhIjjI8uT2IGk=
 github.com/quic-go/qpack v0.4.0 h1:Cr9BXA1sQS2SmDUWjSofMPNKmvF6IiIfDRmgU0w1ZCo=
 github.com/quic-go/qpack v0.4.0/go.mod h1:UZVnYIfi5GRk+zI9UMaCPsmZ2xKJP7XBUvVyT1Knj9A=
+github.com/refraction-networking/clienthellod v0.5.0-alpha2 h1:h4y/a97p9EsxAdhXYCBcf8kGfroJ6sjTQ4F/yJyna4A=
+github.com/refraction-networking/clienthellod v0.5.0-alpha2/go.mod h1:4vN+Qh4x2TznUMsfw6N3ohGjwvfs6lnwwNPUn7zI9bQ=
 github.com/refraction-networking/utls v1.6.6 h1:igFsYBUJPYM8Rno9xUuDoM5GQrVEqY4llzEXOkL43Ig=
 github.com/refraction-networking/utls v1.6.6/go.mod h1:BC3O4vQzye5hqpmDTWUqi4P5DDhzJfkV1tdqtawQIH0=
 github.com/russross/blackfriday v1.5.2/go.mod h1:JO/DiYxRf+HjHt06OyowR9PTA263kcR/rfWxYHBV53g=
@@ -138,11 +136,11 @@ golang.org/x/crypto v0.0.0-20181030102418-4d3f4d9ffa16/go.mod h1:6SG95UA2DQfeDnf
 golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
 golang.org/x/crypto v0.0.0-20190313024323-a1f597ede03a/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
 golang.org/x/crypto v0.0.0-20191011191535-87dc89f01550/go.mod h1:yigFU9vqHzYiE8UmvKecakEJjdnWj3jj499lnFckfCI=
-golang.org/x/crypto v0.22.0 h1:g1v0xeRhjcugydODzvb3mEM9SQ0HGp9s/nh3COQ/C30=
-golang.org/x/crypto v0.22.0/go.mod h1:vr6Su+7cTlO45qkww3VDJlzDn0ctJvRgYbC2NvXHt+M=
+golang.org/x/crypto v0.23.0 h1:dIJU/v2J8Mdglj/8rJ6UUOM3Zc9zLZxVZwwxMooUSAI=
+golang.org/x/crypto v0.23.0/go.mod h1:CKFgDieR+mRhux2Lsu27y0fO304Db0wZe70UKqHu0v8=
 golang.org/x/exp v0.0.0-20190121172915-509febef88a4/go.mod h1:CJ0aWSM057203Lf6IL+f9T1iT9GByDxfZKAQTCR3kQA=
-golang.org/x/exp v0.0.0-20240416160154-fe59bbe5cc7f h1:99ci1mjWVBWwJiEKYY6jWa4d2nTQVIEhZIptnrVb1XY=
-golang.org/x/exp v0.0.0-20240416160154-fe59bbe5cc7f/go.mod h1:/lliqkxwWAhPjf5oSOIJup2XcqJaw8RGS6k3TGEc7GI=
+golang.org/x/exp v0.0.0-20240506185415-9bf2ced13842 h1:vr/HnozRka3pE4EsMEg1lgkXJkTFJCVUX+S/ZT6wYzM=
+golang.org/x/exp v0.0.0-20240506185415-9bf2ced13842/go.mod h1:XtvwrStGgqGPLc4cjQfWqZHG1YFdYs6swckp8vpsjnc=
 golang.org/x/lint v0.0.0-20180702182130-06c8688daad7/go.mod h1:UVdnD1Gm6xHRNCYTkRU2/jEulfH38KcIWyp/GAMgvoE=
 golang.org/x/lint v0.0.0-20181026193005-c67002cb31c3/go.mod h1:UVdnD1Gm6xHRNCYTkRU2/jEulfH38KcIWyp/GAMgvoE=
 golang.org/x/lint v0.0.0-20190227174305-5b3e6a55c961/go.mod h1:wehouNa3lNwaWXcvxsM5YxQ5yQlVC4a0KAMCusXpPoU=
@@ -160,8 +158,8 @@ golang.org/x/net v0.0.0-20190213061140-3a22650c66bd/go.mod h1:mL1N/T3taQHkDXs73r
 golang.org/x/net v0.0.0-20190313220215-9f648a60d977/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
 golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
 golang.org/x/net v0.0.0-20190620200207-3b0461eec859/go.mod h1:z5CRVTTTmAJ677TzLLGU+0bjPO0LkuOLi4/5GtJWs/s=
-golang.org/x/net v0.24.0 h1:1PcaxkF854Fu3+lvBIx5SYn9wRlBzzcnHZSiaFFAb0w=
-golang.org/x/net v0.24.0/go.mod h1:2Q7sJY5mzlzWjKtYUEXSlBWCdyaioyXzRB2RtU8KVE8=
+golang.org/x/net v0.25.0 h1:d/OCCoBEUq33pjydKrGQhw7IlUPI2Oylr+8qLx49kac=
+golang.org/x/net v0.25.0/go.mod h1:JkAGAh7GEvH74S6FOH42FLoXpXbE/aqXSrIQjXgsiwM=
 golang.org/x/oauth2 v0.0.0-20180821212333-d2e6202438be/go.mod h1:N/0e6XlmueqKjAGxoOufVs8QHGRruUQn6yWY3a++T0U=
 golang.org/x/oauth2 v0.0.0-20181017192945-9dcd33a902f4/go.mod h1:N/0e6XlmueqKjAGxoOufVs8QHGRruUQn6yWY3a++T0U=
 golang.org/x/oauth2 v0.0.0-20181203162652-d668ce993890/go.mod h1:N/0e6XlmueqKjAGxoOufVs8QHGRruUQn6yWY3a++T0U=
@@ -180,12 +178,12 @@ golang.org/x/sys v0.0.0-20181029174526-d69651ed3497/go.mod h1:STP8DvDyc/dI5b8T5h
 golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20190316082340-a2f829d7f35f/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20190412213103-97732733099d/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
-golang.org/x/sys v0.19.0 h1:q5f1RH2jigJ1MoAWp2KTp3gm5zAGFUTarQZ5U386+4o=
-golang.org/x/sys v0.19.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
+golang.org/x/sys v0.20.0 h1:Od9JTbYCk261bKm4M/mw7AklTlFYIa0bIp9BgSm1S8Y=
+golang.org/x/sys v0.20.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
 golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
 golang.org/x/text v0.3.1-0.20180807135948-17ff2d5776d2/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
-golang.org/x/text v0.14.0 h1:ScX5w1eTa3QqT8oi6+ziP7dTV1S2+ALU0bI+0zXKWiQ=
-golang.org/x/text v0.14.0/go.mod h1:18ZOQIKpY8NJVqYksKHtTdi31H5itFRjB5/qKTNYzSU=
+golang.org/x/text v0.15.0 h1:h1V/4gjBv8v9cjcR6+AR5+/cIYK5N/WAgiv4xlsEtAk=
+golang.org/x/text v0.15.0/go.mod h1:18ZOQIKpY8NJVqYksKHtTdi31H5itFRjB5/qKTNYzSU=
 golang.org/x/time v0.0.0-20180412165947-fbb02b2291d2/go.mod h1:tRJNPiyCQ0inRvYxbN9jk5I+vvW/OXSQhTDSoE431IQ=
 golang.org/x/time v0.0.0-20181108054448-85acf8d2951c/go.mod h1:tRJNPiyCQ0inRvYxbN9jk5I+vvW/OXSQhTDSoE431IQ=
 golang.org/x/time v0.5.0 h1:o7cqy6amK/52YcAKIPlM3a+Fpj35zvRj2TP+e1xFSfk=
@@ -195,8 +193,8 @@ golang.org/x/tools v0.0.0-20181030000716-a0a13e073c7b/go.mod h1:n7NCudcB/nEzxVGm
 golang.org/x/tools v0.0.0-20190114222345-bf090417da8b/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
 golang.org/x/tools v0.0.0-20190226205152-f727befe758c/go.mod h1:9Yl7xja0Znq3iFh3HoIrodX9oNMXvdceNzlUR8zjMvY=
 golang.org/x/tools v0.0.0-20200130002326-2f3ba24bd6e7/go.mod h1:TB2adYChydJhpapKDTa4BR/hXlZSLoq2Wpct/0txZ28=
-golang.org/x/tools v0.20.0 h1:hz/CVckiOxybQvFw6h7b/q80NTr9IUQb4s1IIzW7KNY=
-golang.org/x/tools v0.20.0/go.mod h1:WvitBU7JJf6A4jOdg4S1tviW9bhUxkgeCui/0JHctQg=
+golang.org/x/tools v0.21.0 h1:qc0xYgIbsSDt9EyWz05J5wfa7LOVW0YTLOXrqdLAWIw=
+golang.org/x/tools v0.21.0/go.mod h1:aiJjzUbINMkxbQROHiO6hDPo2LHcIPhhQsa9DLh0yGk=
 golang.org/x/xerrors v0.0.0-20191011141410-1b5146add898/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
 google.golang.org/api v0.0.0-20180910000450-7ca32eb868bf/go.mod h1:4mhQ8q/RsB7i+udVvVy5NUi08OU8ZlA0gRVgrF7VFY0=
 google.golang.org/api v0.0.0-20181030000543-1d582fd0359e/go.mod h1:4mhQ8q/RsB7i+udVvVy5NUi08OU8ZlA0gRVgrF7VFY0=
@@ -214,8 +212,8 @@ google.golang.org/grpc v1.14.0/go.mod h1:yo6s7OP7yaDglbqo1J04qKzAhqBH6lvTonzMVmE
 google.golang.org/grpc v1.16.0/go.mod h1:0JHn/cJsOMiMfNA9+DeHDlAU7KAAB5GDlYFpa9MZMio=
 google.golang.org/grpc v1.17.0/go.mod h1:6QZJwpn2B+Zp71q/5VxRsJ6NXXVCE5NRUHRo+f3cWCs=
 google.golang.org/grpc v1.19.0/go.mod h1:mqu4LbDTu4XGKhr4mRzUsmM4RtVoemTSY81AxZiDr8c=
-google.golang.org/protobuf v1.33.0 h1:uNO2rsAINq/JlFpSdYEKIZ0uKD/R9cpdv0T+yoGwGmI=
-google.golang.org/protobuf v1.33.0/go.mod h1:c6P6GXX6sHbq/GpV6MGZEdwhWPcYBgnhAHhKbcUYpos=
+google.golang.org/protobuf v1.34.1 h1:9ddQBjfCyZPOHPUiPxpYESBLc+T8P3E+Vo4IbKZgFWg=
+google.golang.org/protobuf v1.34.1/go.mod h1:c6P6GXX6sHbq/GpV6MGZEdwhWPcYBgnhAHhKbcUYpos=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/check.v1 v1.0.0-20201130134442-10cb98267c6c h1:Hei/4ADfdWqJk1ZMxUNpqntNwaWcugrBjAiHlqqRiVk=
 gopkg.in/check.v1 v1.0.0-20201130134442-10cb98267c6c/go.mod h1:JHkPIbrfpd72SG/EVd6muEfDQjcINNoR0C8j2r3qZ4Q=

diff --git a/u_packet_packer.go b/u_packet_packer.go
@@ -4,7 +4,7 @@ import (
 	"bytes"
 	"fmt"
 
-	"github.com/gaukas/clienthellod"
+	"github.com/refraction-networking/clienthellod"
 	"github.com/refraction-networking/uquic/internal/handshake"
 	"github.com/refraction-networking/uquic/internal/protocol"
 	"github.com/refraction-networking/uquic/internal/wire"
@@ -250,8 +250,13 @@ func (p *uPacketPacker) MarshalInitialPacketPayload(pl payload, v protocol.Versi
 		return nil, err
 	}
 
-	if p.uSpec.InitialPacketSpec.FrameBuilder == nil {
+	if p.uSpec.InitialPacketSpec.FrameBuilder == nil || len(p.uSpec.InitialPacketSpec.FrameBuilder.(QUICFrames)) == 0 {
 		qfs := QUICFrames{}
+		for _, frame := range qchframes {
+			if cryptoFrame, ok := frame.(*clienthellod.CRYPTO); ok {
+				qfs = append(qfs, QUICFrameCrypto{int(cryptoFrame.Offset), int(cryptoFrame.Length)})
+			}
+		}
 		return qfs.Build(cryptoData)
 	}
 	return p.uSpec.InitialPacketSpec.FrameBuilder.Build(cryptoData)

diff --git a/u_quic_frames.go b/u_quic_frames.go
@@ -4,10 +4,11 @@ import (
 	"bytes"
 	"crypto/rand"
 	"errors"
+	"math"
 	"math/big"
 	mrand "math/rand"
 
-	"github.com/gaukas/clienthellod"
+	"github.com/refraction-networking/clienthellod"
 	"github.com/refraction-networking/uquic/quicvarint"
 )
 
@@ -30,18 +31,26 @@ func (qfs QUICFrames) Build(cryptoData []byte) (payload []byte, err error) {
 		return qfsCryptoOnly.Build(cryptoData)
 	}
 
+	lowestOffset := math.MaxUint16
+	for _, frame := range qfs {
+		if offset, _, _ := frame.CryptoFrameInfo(); offset < lowestOffset {
+			lowestOffset = offset
+		}
+	}
+
 	for _, frame := range qfs {
 		var frameBytes []byte
 		if offset, length, cryptoOK := frame.CryptoFrameInfo(); cryptoOK {
+			lengthOffset := offset - lowestOffset
 			if length == 0 {
 				// calculate length: from offset to the end of cryptoData
-				length = len(cryptoData) - offset
+				length = len(cryptoData) - lengthOffset
 			}
 			frameBytes = []byte{0x06} // CRYPTO frame type
 			frameBytes = quicvarint.Append(frameBytes, uint64(offset))
 			frameBytes = quicvarint.Append(frameBytes, uint64(length))
 			frameCryptoData := make([]byte, length)
-			copy(frameCryptoData, cryptoData[offset:]) // copy at most length bytes
+			copy(frameCryptoData, cryptoData[lengthOffset:]) // copy at most length bytes
 			frameBytes = append(frameBytes, frameCryptoData...)
 		} else { // Handle none crypto frames: read and append to payload
 			frameBytes, err = frame.Read()

diff --git a/u_quic_frames_test.go b/u_quic_frames_test.go
@@ -4,7 +4,7 @@ import (
 	"bytes"
 	"testing"
 
-	"github.com/gaukas/clienthellod"
+	"github.com/refraction-networking/clienthellod"
 )
 
 func TestQUICFrames(t *testing.T) {