Adversaries may reduce the level of effort required to decrypt data transmitted over the network by reducing the cipher strength of encrypted communications.(Citation: Cisco Synful Knock Evolution)

Adversaries can weaken the encryption software on a compromised network device by reducing the key size used by the software to convert plaintext to ciphertext (e.g., from hundreds or thousands of bytes to just a couple of bytes). As a result, adversaries dramatically reduce the amount of effort needed to decrypt the protected information without the key.

Adversaries may modify the key size used and other encryption parameters using specialized commands in a [Network Device CLI](https://attack.mitre.org/techniques/T1059/008) introduced to the system through [Modify System Image](https://attack.mitre.org/techniques/T1601) to change the configuration of the device. (Citation: Cisco Blog Legacy Device Attacks)
Reduce Key Space
source_name: mitre-attack  url: https://attack.mitre.org/techniques/T1600/001  external_id: T1600.001     source_name: Cisco Synful Knock Evolution  description: Graham Holmes. (2015, October 8). Evolution of attacks on Cisco IOS devices. Retrieved October 19, 2020.  url: https://blogs.cisco.com/security/evolution-of-attacks-on-cisco-ios-devices     source_name: Cisco Blog Legacy Device Attacks  description: Omar Santos. (2020, October 19). Attackers Continue to Target Legacy Devices. Retrieved October 20, 2020.  url: https://community.cisco.com/t5/security-blogs/attackers-continue-to-target-legacy-devices/ba-p/4169954     