Secure Password Encryption - Cisco ASR 5000 Series Administration Manual

System Security

Secure Password Encryption

By default for StarOS releases prior to 21.0 the system encrypts passwords using an MD5-based cipher (option
A). These passwords also have a random 64-bit (8-byte) salt added to the password. The chassis key is used
as the encryption key.
Setting a chassis key supports an encryption method where the decryption requires the knowledge of a "shared
secret". Only a chassis with knowledge of this shared secret can access the passwords. To decipher passwords,
a hacker who knew the chassis key would still need to identify the location of the 64-bit random salt value
within the encryption.
Passwords encrypted with MD-5 will have "+A" prefixes in the configuration file to identify the methodology
used for encrypting.
Important
For release 15.0 and higher, another type of encryption algorithm can be specified. The Global Configuration
mode cli-encrypt-algorithm command allows an operator to configure the password/secret encryption
algorithm. The default encryption/password algorithm for releases prior to 21.0 is MD-5 as described above
(option A). A second password encryption algorithm (option B) uses AES-CTR-128 for encryption and
HMAC-SHA1 for authentication. The encryption key protects the confidentiality of passwords, while the
authentication key protects their integrity. For release 21.0 and higher Algorithm B is the default. Passwords
encrypted with this key will have "+B" prefixes in the configuration file.
For release 19.2 and higher, a third type of encryption algorithm can be specified (option C). This algorithm
specifies the use of the HMAC-SHA512 cipher algorithm for encryption and authentication. Passwords
encrypted with this key will have "+C" prefixes in the configuration file.
Also for release 19.2 and higher, the encryption key is hashed from the chassis ID and a 16-byte Initialization
Vector (IV) obtained from an internal random number generator. No two passwords are encrypted using the
same encryption key/IV pair. The Security Administrator must set a chassis key in order to generate the chassis
ID and resulting encryption key. A default chassis key based on a local MAC address is no longer supported.
The syntax for the cli-encrypt-algorithm command is:
config
cli-encrypt-algorithm { A | B | C }
Support for Non-Current Encryptions and Decryptions
The system supports previously formatted encrypted passwords. The syntax of the encrypted passwords
indicates which methodology was used for encryption. If the system does not see a prefix before the encrypted
password, the earlier encryption method using a fixed key will be used. If the encrypted password includes
the "+A" prefix, the decryption method uses the chassis key and random salt.
If the user saves a new configuration, the generated file will always contain passwords encrypted by the most
recent method. The user cannot generate the earlier DES-based encryption values. However, all future StarOS
releases will continue to support plain-text password entry for all two-way encryptable passwords
The recommended process for changing the chassis key without causing a "lock-out" state is as follows:
• Load the configuration file of the last good configuration using the previous chassis key.
For release 21.0 and higher, the default is Algorithm B.
ASR 5500 System Administration Guide, StarOS Release 21.4
Secure Password Encryption
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