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T1573.002 Asymmetric Cryptography

Adversaries may employ a known asymmetric encryption algorithm to conceal command and control traffic rather than relying on any inherent protections provided by a communication protocol. Asymmetric cryptography, also known as public key cryptography, uses a keypair per party: one public that can be freely distributed, and one private. Due to how the keys are generated, the sender encrypts data with the receiver’s public key and the receiver decrypts the data with their private key. This ensures that only the intended recipient can read the encrypted data. Common public key encryption algorithms include RSA and ElGamal.

For efficiency, many protocols (including SSL/TLS) use symmetric cryptography once a connection is established, but use asymmetric cryptography to establish or transmit a key. As such, these protocols are classified as Asymmetric Cryptography.

Item Value
ID T1573.002
Sub-techniques T1573.001, T1573.002
Tactics TA0011
Platforms Linux, Windows, macOS
Version 1.0
Created 16 March 2020
Last Modified 20 April 2021

Procedure Examples

ID Name Description
S0202 adbupd adbupd contains a copy of the OpenSSL library to encrypt C2 traffic.53
S0045 ADVSTORESHELL A variant of ADVSTORESHELL encrypts some C2 with RSA.51
S0438 Attor Attor‘s Blowfish key is encrypted with a public RSA key.29
S0534 Bazar Bazar can use TLS in C2 communications.41
S0017 BISCUIT BISCUIT uses SSL for encrypting C2 communications.44
C0021 C0021 During C0021, the threat actors used SSL via TCP port 443 for C2 communications.76
S0335 Carbon Carbon has used RSA encryption for C2 communications.50
S0023 CHOPSTICK CHOPSTICK encrypts C2 communications with TLS.40
G0080 Cobalt Group Cobalt Group has used the Plink utility to create SSH tunnels.73
S0154 Cobalt Strike Cobalt Strike can use RSA asymmetric encryption with PKCS1 padding to encrypt data sent to the C2 server.16
S0126 ComRAT ComRAT can use SSL/TLS encryption for its HTTP-based C2 channel. ComRAT has used public key cryptography with RSA and AES encrypted email attachments for its Gmail C2 channel.3839
S0687 Cyclops Blink Cyclops Blink can encrypt C2 messages with AES-256-CBC sent underneath TLS. OpenSSL library functions are also used to encrypt each message using a randomly generated key and IV, which are then encrypted using a hard-coded RSA public key.43
S0673 DarkWatchman DarkWatchman can use TLS to encrypt its C2 channel.21
S0600 Doki Doki has used the embedTLS library for network communications.46
S0384 Dridex Dridex has encrypted traffic with RSA.22
S0367 Emotet Emotet is known to use RSA keys for encrypting C2 traffic. 37
S0363 Empire Empire can use TLS to encrypt its C2 channel.4
G0037 FIN6 FIN6 used the Plink command-line utility to create SSH tunnels to C2 servers.75
G0061 FIN8 FIN8 has used the Plink utility to tunnel RDP back to C2 infrastructure.70
S0168 Gazer Gazer uses custom encryption for C2 that uses RSA.6061
S0588 GoldMax GoldMax has RSA-encrypted its communication with the C2 server.30
S0531 Grandoreiro Grandoreiro can use SSL in C2 communication.49
S0342 GreyEnergy GreyEnergy encrypts communications using RSA-2048.64
S0632 GrimAgent GrimAgent can use a hardcoded server public RSA key to encrypt the first request to C2.47
S0087 Hi-Zor Hi-Zor encrypts C2 traffic with TLS.31
S0483 IcedID IcedID has used SSL and TLS in communications with C2.1415
S1051 KEYPLUG KEYPLUG can use TLS-encrypted WebSocket Protocol (WSS) for C2.48
S0250 Koadic Koadic can use SSL and TLS for communications.5
S0641 Kobalos Kobalos‘s authentication and key exchange is performed using RSA-512.6768
S0409 Machete Machete has used TLS-encrypted FTP to exfiltrate data.63
S0455 Metamorfo Metamorfo‘s C2 communication has been encrypted using OpenSSL.52
S0699 Mythic Mythic supports SSL encrypted C2.6
G0049 OilRig OilRig used the Plink utility and other tools to create tunnels to C2 servers.74
C0014 Operation Wocao During Operation Wocao, threat actors’ proxy implementation “Agent” upgraded the socket in use to a TLS socket.77
S0556 Pay2Key Pay2Key has used RSA encrypted communications with C2.13
S0587 Penquin Penquin can encrypt communications using the BlowFish algorithm and a symmetric key exchanged with Diffie Hellman.59
S0428 PoetRAT PoetRAT used TLS to encrypt command and control (C2) communications.20
S0150 POSHSPY POSHSPY encrypts C2 traffic with AES and RSA.19
S0223 POWERSTATS POWERSTATS has encrypted C2 traffic with RSA.27
S0192 Pupy Pupy‘s default encryption for its C2 communication channel is SSL, but it also has transport options for RSA and AES.11
S0496 REvil REvil has encrypted C2 communications with the ECIES algorithm.18
S0448 Rising Sun Rising Sun variants can use SSL for encrypting C2 communications.17
S0382 ServHelper ServHelper may set up a reverse SSH tunnel to give the attacker access to services running on the victim, such as RDP.12
S0633 Sliver Sliver can use mutual TLS and RSA cryptography to exchange a session key.789
S1035 Small Sieve Small Sieve can use SSL/TLS for its HTTPS Telegram Bot API-based C2 channel.69
S0627 SodaMaster SodaMaster can use a hardcoded RSA key to encrypt some of its C2 traffic.58
S0615 SombRAT SombRAT can SSL encrypt C2 traffic.232425
S0491 StrongPity StrongPity has encrypted C2 traffic using SSL/TLS.32
S0018 Sykipot Sykipot uses SSL for encrypting C2 communications.65
S0668 TinyTurla TinyTurla has the ability to encrypt C2 traffic with SSL/TLS.66
S0183 Tor Tor encapsulates traffic in multiple layers of encryption, using TLS by default.10
S0094 Trojan.Karagany Trojan.Karagany can secure C2 communications with SSL and TLS.54
G0081 Tropic Trooper Tropic Trooper has used SSL to connect to C2 servers.7172
S0180 Volgmer Some Volgmer variants use SSL to encrypt C2 communications.28
S0366 WannaCry WannaCry uses Tor for command and control traffic and routes a custom cryptographic protocol over the Tor circuit.26
S0515 WellMail WellMail can use hard coded client and certificate authority certificates to communicate with C2 over mutual TLS.6236
S0514 WellMess WellMess can communicate to C2 with mutual TLS where client and server mutually check certificates.33343536
S1065 Woody RAT Woody RAT can use RSA-4096 to encrypt data sent to its C2 server.42
S0117 XTunnel XTunnel uses SSL/TLS and RC4 to encrypt traffic.4540
S0251 Zebrocy Zebrocy uses SSL and AES ECB for encrypting C2 communications.555657

Mitigations

ID Mitigation Description
M1031 Network Intrusion Prevention Network intrusion detection and prevention systems that use network signatures to identify traffic for specific adversary malware can be used to mitigate activity at the network level.
M1020 SSL/TLS Inspection SSL/TLS inspection can be used to see the contents of encrypted sessions to look for network-based indicators of malware communication protocols.

Detection

ID Data Source Data Component
DS0029 Network Traffic Network Traffic Content

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