Great news! Belkasoft supports keychain extraction from iOS devices. In addition, Signal iOS app decryption is supported.
The new feature is available in Belkasoft Evidence Center v.9.9800.4928 with checkm8. Keychain is extracted either in the process of iPhone acquisition using #checkm8 method built-in Evidence Center or, if you have a jailbroken iPhone, keychain will also be extracted no matter what jailbreak was used.
The Signal chat extraction and decryption are based on acquired keychain data.