diff options
author | Yawning Angel <yawning@torproject.org> | 2015-02-17 11:33:29 +0000 |
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committer | Yawning Angel <yawning@torproject.org> | 2015-02-17 11:33:29 +0000 |
commit | 0066cfc3932c50323fa596981f18ef5b0e862742 (patch) | |
tree | 49ac284ec91fe342a1995693b9bc7d3e015eee8e /transports/scramblesuit/hkdf_expand.go | |
parent | 0f038ca4fa4c175d427251838cfee6fb6d6b9e2f (diff) |
Add support for acting as a ScrambleSuit client.
This allows obfs4proxy to be used as a ScrambleSuit client that is wire
compatible with the obfs4proxy implementation, including session ticket
support, and length obfuscation.
The current implementation has the following limitations:
* IAT obfuscation is not supported (and is disabled in all other
ScrambleSuit implementations by default).
* The length distribution and probabilites are different from those
generated by obfsproxy and obfsclient due to a different DRBG.
* Server support is missing and is unlikely to be implemented.
Diffstat (limited to 'transports/scramblesuit/hkdf_expand.go')
-rw-r--r-- | transports/scramblesuit/hkdf_expand.go | 67 |
1 files changed, 67 insertions, 0 deletions
diff --git a/transports/scramblesuit/hkdf_expand.go b/transports/scramblesuit/hkdf_expand.go new file mode 100644 index 0000000..9626b38 --- /dev/null +++ b/transports/scramblesuit/hkdf_expand.go @@ -0,0 +1,67 @@ +/* + * Copyright (c) 2015, Yawning Angel <yawning at torproject dot org> + * All rights reserved. + * + * Redistribution and use in source and binary forms, with or without + * modification, are permitted provided that the following conditions are met: + * + * * Redistributions of source code must retain the above copyright notice, + * this list of conditions and the following disclaimer. + * + * * Redistributions in binary form must reproduce the above copyright notice, + * this list of conditions and the following disclaimer in the documentation + * and/or other materials provided with the distribution. + * + * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" + * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE + * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE + * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE + * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR + * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF + * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS + * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN + * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) + * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE + * POSSIBILITY OF SUCH DAMAGE. + */ + +package scramblesuit + +import ( + "crypto/hmac" + "hash" +) + +func hkdfExpand(hashFn func() hash.Hash, prk []byte, info []byte, l int) []byte { + // Why, yes. golang.org/x/crypto/hkdf exists, and is a fine + // implementation of HKDF. However it does both the extract + // and expand, while ScrambleSuit only does extract, with no + // way to separate the two steps. + + h := hmac.New(hashFn, prk) + digestSz := h.Size() + if l > 255*digestSz { + panic("hkdf: requested OKM length > 255*HashLen") + } + + var t []byte + okm := make([]byte, 0, l) + toAppend := l + ctr := byte(1) + for toAppend > 0 { + h.Reset() + h.Write(t) + h.Write(info) + h.Write([]byte{ctr}) + t = h.Sum(nil) + ctr++ + + aLen := digestSz + if toAppend < digestSz { + aLen = toAppend + } + okm = append(okm, t[:aLen]...) + toAppend -= aLen + } + return okm +} |