This can be done as a post-installation task.
The value for the encryption algorithm is stored in the edsaRGSKCryptoAlgorithm attribute which is found in the Advanced Properties of the Administration Services container found under Configuration | Server Configuration | Administration Services .
It is not possible to configure this value via the Active Roles Console, but it is possible to do so using the Active Roles Management Shell, as follows:
Reset-AREncryptionKey -EncryptionAlgorithm 'AES'
Reset-AREncryptionKey -EncryptionAlgorithm 'DES'
NOTE: It is important to run the Active Roles Management Shell as a local Administrator who is also an Active Roles Admin. Otherwise, attempting to execute the above cmdlet will fail with the following error:
Running the above cmdlet will automatically generate a new encryption key. This new key can then be backed up using the Backup-AREncryptionKey cmdlet.
With ActiveRoles Server 6.9 and previous versions, the default value for this attribute is 3DES-192.