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AES-GCM runtime availability check, Advertise / initialize AES-GCM cipher only if supported #197

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AES-GCM runtime availability check, Advertise / initialize AES-GCM cipher only if supported #197

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410959c
AES-GCM runtime availability check
past-due Oct 17, 2021
9210335
crypto_bcrypt.cpp: Initialize hAlgAES
past-due Oct 17, 2021
b775c2b
Advertise / initialize AES_GCM cipher only if supported
past-due Oct 17, 2021
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42 changes: 29 additions & 13 deletions src/steamnetworkingsockets/clientlib/steamnetworkingsockets_connections.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1037,14 +1037,17 @@ void CSteamNetworkConnectionBase::ClearCrypto()
void CSteamNetworkConnectionBase::ClearLocalCrypto()
{
AssertLocksHeldByCurrentThread();
m_eNegotiatedCipher = k_ESteamNetworkingSocketsCipher_INVALID;
m_cbEncryptionOverhead = k_cbAESGCMTagSize;
m_keyExchangePrivateKeyLocal.Wipe();
m_msgCryptLocal.Clear();
m_msgSignedCryptLocal.Clear();
m_bCryptKeysValid = false;
m_cryptContextSend.Wipe();
m_cryptContextRecv.Wipe();
if (m_eNegotiatedCipher != k_ESteamNetworkingSocketsCipher_NULL)
{
m_cryptContextSend.Wipe();
m_cryptContextRecv.Wipe();
}
m_eNegotiatedCipher = k_ESteamNetworkingSocketsCipher_INVALID;
m_cbEncryptionOverhead = k_cbAESGCMTagSize;
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@zpostfacto zpostfacto Oct 18, 2021 •
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It should be legal to always wipe these, even if they aren't initialized?

Stepping back:

If we're going to support more than one cipher we need to refactor this. because m_cryptContextSend is too generic of a name if it is always going to be an instance of AES-GCM. We probably should add a new abstract interface ISymmetricEncryptContext, with two virtual methods, Encrypt() and the destructor. We would never "wipe" a context, we would just delete it, and the destructor would always securely wipe it. AES_GCM_EncryptContext would implement this interface. (The old mix-in interface design pattern --- yes, multiple-base classes.) So then we would have std::unique_ptr<ISymmetricEncryptContext> m_pEncryptContext. (And the same for decrypt.) So you would deal in concrete types when you were initializing, but once initialization was complete, you would just have the abstract type.

There's a lot of stuff going on in the Steam branch that needs to be merged and cleaned up in crypto land (recently upgraded to a new version of OpenSSL), but if you want to take a stab at it, I can pull that and then I can clean this up when I get back in sync with Steam.

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I'd debated that, but I wasn't sure how extensive a refactor would be eagerly welcomed. 😄

Will take a look when I have a moment. 👍

m_cryptIVSend.Wipe();
m_cryptIVRecv.Wipe();
}
Expand Down Expand Up @@ -1219,19 +1222,29 @@ void CSteamNetworkConnectionBase::SetCryptoCipherList()
// V
case 0:
// Not allowed
m_msgCryptLocal.add_ciphers( k_ESteamNetworkingSocketsCipher_AES_256_GCM );
if (AES_GCM_CipherContext::IsAvailable())
{
m_msgCryptLocal.add_ciphers( k_ESteamNetworkingSocketsCipher_AES_256_GCM );
}
Assert( m_msgCryptLocal.ciphers_size() > 0 );
break;
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@zpostfacto zpostfacto Oct 18, 2021 •
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I think this situation should be fatal to the connection. (If the connection is configured to require encryption, it should be fatal if encryption is not available.)


case 1:
// Allowed, but prefer encrypted
m_msgCryptLocal.add_ciphers( k_ESteamNetworkingSocketsCipher_AES_256_GCM );
if (AES_GCM_CipherContext::IsAvailable())
{
m_msgCryptLocal.add_ciphers( k_ESteamNetworkingSocketsCipher_AES_256_GCM );
}
m_msgCryptLocal.add_ciphers( k_ESteamNetworkingSocketsCipher_NULL );
break;

case 2:
// Allowed, preferred
m_msgCryptLocal.add_ciphers( k_ESteamNetworkingSocketsCipher_NULL );
m_msgCryptLocal.add_ciphers( k_ESteamNetworkingSocketsCipher_AES_256_GCM );
if (AES_GCM_CipherContext::IsAvailable())
{
m_msgCryptLocal.add_ciphers( k_ESteamNetworkingSocketsCipher_AES_256_GCM );
}
break;

case 3:
Expand Down Expand Up @@ -1693,13 +1706,16 @@ bool CSteamNetworkConnectionBase::BFinishCryptoHandshake( bool bServer )
V_memcpy( pStart, &expandTemp, sizeof(SHA256Digest_t) );
}

// Set encryption keys into the contexts, and set parameters
if (
!m_cryptContextSend.Init( cryptKeySend.m_buf, cryptKeySend.k_nSize, m_cryptIVSend.k_nSize, k_cbAESGCMTagSize )
|| !m_cryptContextRecv.Init( cryptKeyRecv.m_buf, cryptKeyRecv.k_nSize, m_cryptIVRecv.k_nSize, k_cbAESGCMTagSize ) )
if (m_eNegotiatedCipher != k_ESteamNetworkingSocketsCipher_NULL)
{
ConnectionState_ProblemDetectedLocally( k_ESteamNetConnectionEnd_Remote_BadCrypt, "Error initializing crypto" );
return false;
// Set encryption keys into the contexts, and set parameters
if (
!m_cryptContextSend.Init( cryptKeySend.m_buf, cryptKeySend.k_nSize, m_cryptIVSend.k_nSize, k_cbAESGCMTagSize )
|| !m_cryptContextRecv.Init( cryptKeyRecv.m_buf, cryptKeyRecv.k_nSize, m_cryptIVRecv.k_nSize, k_cbAESGCMTagSize ) )
{
ConnectionState_ProblemDetectedLocally( k_ESteamNetConnectionEnd_Remote_BadCrypt, "Error initializing crypto" );
return false;
}
}

//
Expand Down