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ssh: add support for FIPS mode

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Unsupported algoritms are silently ignored and not negotiated, or
rejected

Fixes golang/go#75061

Change-Id: I08d50d10a97c08e78aedead89ca61beceff88918
Reviewed-on: https://go-review.googlesource.com/c/crypto/+/698795
Reviewed-by: Mio Mio <miomio0086@gmail.com>
Reviewed-by: Junyang Shao <shaojunyang@google.com>
Reviewed-by: Filippo Valsorda <filippo@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
This commit is contained in:
Nicola Murino
2025-09-27 12:36:52 -07:00
parent ddb4e80c6a
commit 66c3d8ce71
8 changed files with 163 additions and 69 deletions
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ssh/cipher.go
+29 -27
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@@ -8,6 +8,7 @@ import (
"crypto/aes"
"crypto/cipher"
"crypto/des"
"crypto/fips140"
"crypto/rc4"
"crypto/subtle"
"encoding/binary"
@@ -15,6 +16,7 @@ import (
"fmt"
"hash"
"io"
"slices"
"golang.org/x/crypto/chacha20"
"golang.org/x/crypto/internal/poly1305"
@@ -93,41 +95,41 @@ func streamCipherMode(skip int, createFunc func(key, iv []byte) (cipher.Stream,
}
// cipherModes documents properties of supported ciphers. Ciphers not included
// are not supported and will not be negotiated, even if explicitly requested in
// ClientConfig.Crypto.Ciphers.
var cipherModes = map[string]*cipherMode{
// Ciphers from RFC 4344, which introduced many CTR-based ciphers. Algorithms
// are defined in the order specified in the RFC.
CipherAES128CTR: {16, aes.BlockSize, streamCipherMode(0, newAESCTR)},
CipherAES192CTR: {24, aes.BlockSize, streamCipherMode(0, newAESCTR)},
CipherAES256CTR: {32, aes.BlockSize, streamCipherMode(0, newAESCTR)},
// are not supported and will not be negotiated, even if explicitly configured.
// When FIPS mode is enabled, only FIPS-approved algorithms are included.
var cipherModes = map[string]*cipherMode{}
// Ciphers from RFC 4345, which introduces security-improved arcfour ciphers.
// They are defined in the order specified in the RFC.
InsecureCipherRC4128: {16, 0, streamCipherMode(1536, newRC4)},
InsecureCipherRC4256: {32, 0, streamCipherMode(1536, newRC4)},
func init() {
cipherModes[CipherAES128CTR] = &cipherMode{16, aes.BlockSize, streamCipherMode(0, newAESCTR)}
cipherModes[CipherAES192CTR] = &cipherMode{24, aes.BlockSize, streamCipherMode(0, newAESCTR)}
cipherModes[CipherAES256CTR] = &cipherMode{32, aes.BlockSize, streamCipherMode(0, newAESCTR)}
// Use of GCM with arbitrary IVs is not allowed in FIPS 140-only mode,
// we'll wire it up to NewGCMForSSH in Go 1.26.
//
// For now it means we'll work with fips140=on but not fips140=only.
cipherModes[CipherAES128GCM] = &cipherMode{16, 12, newGCMCipher}
cipherModes[CipherAES256GCM] = &cipherMode{32, 12, newGCMCipher}
// Cipher defined in RFC 4253, which describes SSH Transport Layer Protocol.
// Note that this cipher is not safe, as stated in RFC 4253: "Arcfour (and
// RC4) has problems with weak keys, and should be used with caution."
// RFC 4345 introduces improved versions of Arcfour.
InsecureCipherRC4: {16, 0, streamCipherMode(0, newRC4)},
// AEAD ciphers
CipherAES128GCM: {16, 12, newGCMCipher},
CipherAES256GCM: {32, 12, newGCMCipher},
CipherChaCha20Poly1305: {64, 0, newChaCha20Cipher},
if fips140.Enabled() {
defaultCiphers = slices.DeleteFunc(defaultCiphers, func(algo string) bool {
_, ok := cipherModes[algo]
return !ok
})
return
}
cipherModes[CipherChaCha20Poly1305] = &cipherMode{64, 0, newChaCha20Cipher}
// Insecure ciphers not included in the default configuration.
cipherModes[InsecureCipherRC4128] = &cipherMode{16, 0, streamCipherMode(1536, newRC4)}
cipherModes[InsecureCipherRC4256] = &cipherMode{32, 0, streamCipherMode(1536, newRC4)}
cipherModes[InsecureCipherRC4] = &cipherMode{16, 0, streamCipherMode(0, newRC4)}
// CBC mode is insecure and so is not included in the default config.
// (See https://www.ieee-security.org/TC/SP2013/papers/4977a526.pdf). If absolutely
// needed, it's possible to specify a custom Config to enable it.
// You should expect that an active attacker can recover plaintext if
// you do.
InsecureCipherAES128CBC: {16, aes.BlockSize, newAESCBCCipher},
// 3des-cbc is insecure and is not included in the default
// config.
InsecureCipherTripleDESCBC: {24, des.BlockSize, newTripleDESCBCCipher},
cipherModes[InsecureCipherAES128CBC] = &cipherMode{16, aes.BlockSize, newAESCBCCipher}
cipherModes[InsecureCipherTripleDESCBC] = &cipherMode{24, des.BlockSize, newTripleDESCBCCipher}
}
// prefixLen is the length of the packet prefix that contains the packet length