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ssh: ignore MAC if AEAD ciphers negotiated

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If the server/client cipher chosen is one of the two AEAD ciphers that
we support (aes128-gcm@openssh.com and chacha20-poly1305@openssh.com),
don't attempt to find a common MAC algorithm in findAgreedAlgorithms.
Similarly in newPacketCipher, don't attempt to generate a MAC key if we
are using a AEAD cipher.

Fixes golang/go#51406

Change-Id: Id48ae72f052cb0a0c597b32e9901a0f218e4161f
Reviewed-on: https://go-review.googlesource.com/c/crypto/+/389214
Trust: Roland Shoemaker <roland@golang.org>
Run-TryBot: Roland Shoemaker <roland@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Filippo Valsorda <filippo@golang.org>
This commit is contained in:
Roland Shoemaker
2022-03-12 13:11:42 +00:00
committed by Filippo Valsorda
parent efcb8507fb
commit 6068a2e6cf
3 changed files with 45 additions and 9 deletions
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ssh/common.go
+15 -6
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@@ -152,6 +152,11 @@ func (a *directionAlgorithms) rekeyBytes() int64 {
return 1 << 30
}
var aeadCiphers = map[string]bool{
gcmCipherID: true,
chacha20Poly1305ID: true,
}
type algorithms struct {
kex string
hostKey string
@@ -187,14 +192,18 @@ func findAgreedAlgorithms(isClient bool, clientKexInit, serverKexInit *kexInitMs
return
}
ctos.MAC, err = findCommon("client to server MAC", clientKexInit.MACsClientServer, serverKexInit.MACsClientServer)
if err != nil {
return
if !aeadCiphers[ctos.Cipher] {
ctos.MAC, err = findCommon("client to server MAC", clientKexInit.MACsClientServer, serverKexInit.MACsClientServer)
if err != nil {
return
}
}
stoc.MAC, err = findCommon("server to client MAC", clientKexInit.MACsServerClient, serverKexInit.MACsServerClient)
if err != nil {
return
if !aeadCiphers[stoc.Cipher] {
stoc.MAC, err = findCommon("server to client MAC", clientKexInit.MACsServerClient, serverKexInit.MACsServerClient)
if err != nil {
return
}
}
ctos.Compression, err = findCommon("client to server compression", clientKexInit.CompressionClientServer, serverKexInit.CompressionClientServer)