.FIPS mode now supports the `aes128-cts-hmac-sha1-96` and `aes256-cts-hmac-sha1-96` encryption types
Previously, Kerberos could not use the `aes128-cts-hmac-sha1-96` and `aes256-cts-hmac-sha1-96` encryption types in FIPS mode on RHEL 9 because the SHA-1 hash algorithm is deprecated in RHEL 9.
With this release, the KRB5KDF key derivation function has been modified and the `FIPS:AD-SUPPORT` crypto subpolicy has been changed to enable `aes128-cts-hmac-sha1-96` and `aes256-cts-hmac-sha1-96` in FIPS mode.
As a result, with the `FIPS:AD-SUPPORT` crypto-policy enabled, the Kerberos Key Distribution Center (KDC) can use the two encryption types to achieve the following:
* Create a KDC database.
* Create keys for Kerberos principals.
* Use the keys for the communication between the client and the KDC.
Enabling the `FIPS:AD-SUPPORT` crypto-policy is required if your systems are integrated into Active Directory. Note that `FIPS:AD-SUPPORT` does not support the `arcfour-hmac-md5` cipher. If this cipher is needed, enable it with the `FIPS:AD-SUPPORT-LEGACY` support policy.
Description of problem:
It is not possible to create a KDC db with the help of "kdb5_util" when the default master_key_type (aes256-cts-hmac-sha1-96) is used.
Version-Release number of selected component (if applicable):
krb5-server-1.19.1-13.el9.x86_64
openssl-3.0.0-6.el9.x86_64
RHEL-9.0.0-20220110.3
How reproducible:
Steps to Reproduce:
1. hostnamectl set-hostname kerberos.example.com
2. sed -i "1i 127.0.0.1 kerberos.example.com" /etc/hosts
3. echo -ne '[realms]\nEXAMPLE.COM = {\n kdc = kerberos.example.com\n admin_server = kerberos.example.com\n}\n\n[domain_realm]\n.example.com = EXAMPLE.COM\nexample.com = example.com\n' > /etc/krb5.conf.d/example_com
4. sed -i "s/^# default_realm/ default_realm/" /etc/krb5.conf
5. modify /var/kerberos/krb5kdc/kdc.conf
...
supported_enctypes = aes256-sha2:normal
...
Actual results:
#kdb5_util create -r EXAMPLE.COM -P password -k aes256-cts-hmac-sha1-96
Loading random data
Initializing database '/var/kerberos/krb5kdc/principal' for realm 'EXAMPLE.COM',
master key name 'K/M'
kdb5_util: Cryptosystem internal error while transforming master key from password
Expected results:
The KDC db should be created because "hmac-sha1-96" will be supported in FIPS mode.
Additional info:
- Works with aes256-cts-hmac-sha384-192:
# kdb5_util create -r EXAMPLE.COM -P password -k aes256-cts-hmac-sha384-192
Loading random data
Initializing database '/var/kerberos/krb5kdc/principal' for realm 'EXAMPLE.COM',
master key name 'K/M'
Not really no.
Unfortunately the Krb5 KDF is not an approved KDF, so the krb5 code needs to either explictly opt out of FIPS mode, or simply accept this limitation in FIPS mode.
Comment 5Alexander Bokovoy
2022-01-13 17:54:51 UTC
From Simo on IRC:
"pass the -fips property when instantiating the KDF for now, until we can find a way to have it in the fips provider"
This is to explicitly get out of FIPS policy use for krb5kdc.
I confirm that passing the "-fips" property when retrieving the default KRB5 KDF does the trick. But if we take this decision, the KDC will not be FIPS-compliant.
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.
For information on the advisory (new packages: krb5), and where to find the updated
files, follow the link below.
If the solution does not work for you, open a new bug report.
https://access.redhat.com/errata/RHBA-2022:3951
Description of problem: It is not possible to create a KDC db with the help of "kdb5_util" when the default master_key_type (aes256-cts-hmac-sha1-96) is used. Version-Release number of selected component (if applicable): krb5-server-1.19.1-13.el9.x86_64 openssl-3.0.0-6.el9.x86_64 RHEL-9.0.0-20220110.3 How reproducible: Steps to Reproduce: 1. hostnamectl set-hostname kerberos.example.com 2. sed -i "1i 127.0.0.1 kerberos.example.com" /etc/hosts 3. echo -ne '[realms]\nEXAMPLE.COM = {\n kdc = kerberos.example.com\n admin_server = kerberos.example.com\n}\n\n[domain_realm]\n.example.com = EXAMPLE.COM\nexample.com = example.com\n' > /etc/krb5.conf.d/example_com 4. sed -i "s/^# default_realm/ default_realm/" /etc/krb5.conf 5. modify /var/kerberos/krb5kdc/kdc.conf ... supported_enctypes = aes256-sha2:normal ... Actual results: #kdb5_util create -r EXAMPLE.COM -P password -k aes256-cts-hmac-sha1-96 Loading random data Initializing database '/var/kerberos/krb5kdc/principal' for realm 'EXAMPLE.COM', master key name 'K/M' kdb5_util: Cryptosystem internal error while transforming master key from password Expected results: The KDC db should be created because "hmac-sha1-96" will be supported in FIPS mode. Additional info: - Works with aes256-cts-hmac-sha384-192: # kdb5_util create -r EXAMPLE.COM -P password -k aes256-cts-hmac-sha384-192 Loading random data Initializing database '/var/kerberos/krb5kdc/principal' for realm 'EXAMPLE.COM', master key name 'K/M'