MIT Kerberos features

Quick facts

License - MIT Kerberos License information

Supported platforms / OS distributions:
  • Windows (KfW 4.0): Windows 7, Vista, XP
  • Solaris: SPARC, x86_64/x86
  • GNU/Linux: Debian x86_64/x86, Ubuntu x86_64/x86, RedHat x86_64/x86
  • BSD: NetBSD x86_64/x86
Crypto backends:

Database backends: LDAP, DB2

krb4 support: Kerberos 5 release < 1.8

DES support: configurable (See Retiring DES)



Starting from release 1.7:

  • Follow client principal referrals in the client library when obtaining initial tickets.
  • KDC can issue realm referrals for service principals based on domain names.
  • Extensions supporting DCE RPC, including three-leg GSS context setup and unencapsulated GSS tokens inside SPNEGO.
  • Microsoft GSS_WrapEX, implemented using the gss_iov API, which is similar to the equivalent SSPI functionality. This is needed to support some instances of DCE RPC.
  • NTLM recognition support in GSS-API, to facilitate dropping in an NTLM implementation for improved compatibility with older releases of Microsoft Windows.
  • KDC support for principal aliases, if the back end supports them. Currently, only the LDAP back end supports aliases.
  • Support Microsoft set/change password (RFC 3244) protocol in kadmind.
  • Implement client and KDC support for GSS_C_DELEG_POLICY_FLAG, which allows a GSS application to request credential delegation only if permitted by KDC policy.

Starting from release 1.8:

  • Microsoft Services for User (S4U) compatibility


  • Support for KCM credential cache starting from release 1.13

Feature list

For more information on the specific project see

Release 1.7
Release 1.8
Release 1.9
  • Advance warning on password expiry
  • Camellia encryption (CTS-CMAC mode) RFC 6803
  • KDC support for SecurID preauthentication
  • kadmin over IPv6
  • Trace logging Trace logging
  • GSSAPI/KRB5 multi-realm support
  • Plugin to test password quality Password quality interface (pwqual)
  • Plugin to synchronize password changes KADM5 hook interface (kadm5_hook)
  • Parallel KDC
  • GSS-API extentions for SASL GS2 bridge RFC 5801 RFC 5587
  • Purging old keys
  • Naming extensions for delegation chain
  • Password expiration API
  • Windows client support (build-only)
  • IPv6 support in iprop
Release 1.10
Release 1.11
  • Client support for FAST OTP RFC 6560
  • GSS-API extensions for credential locations
  • Responder mechanism
Release 1.12

Release 1.13

  • Add support for accessing KDCs via an HTTPS proxy server using the MS-KKDCP protocol.
  • Add support for hierarchical incremental propagation, where slaves can act as intermediates between an upstream master and other downstream slaves.
  • Add support for configuring GSS mechanisms using /etc/gss/mech.d/*.conf files in addition to /etc/gss/mech.
  • Add support to the LDAP KDB module for binding to the LDAP server using SASL.
  • The KDC listens for TCP connections by default.
  • Fix a minor key disclosure vulnerability where using the “keepold” option to the kadmin randkey operation could return the old keys. [CVE-2014-5351]
  • Add client support for the Kerberos Cache Manager protocol. If the host is running a Heimdal kcm daemon, caches served by the daemon can be accessed with the KCM: cache type.
  • When built on macOS 10.7 and higher, use “KCM:” as the default cachetype, unless overridden by command-line options or krb5-config values.
  • Add support for doing unlocked database dumps for the DB2 KDC back end, which would allow the KDC and kadmind to continue accessing the database during lengthy database dumps.

Release 1.14

  • Administrator experience
    • Add a new kdb5_util tabdump command to provide reporting-friendly tabular dump formats (tab-separated or CSV) for the KDC database. Unlike the normal dump format, each output table has a fixed number of fields. Some tables include human-readable forms of data that are opaque in ordinary dump files. This format is also suitable for importing into relational databases for complex queries.
    • Add support to kadmin and kadmin.local for specifying a single command line following any global options, where the command arguments are split by the shell–for example, “kadmin getprinc principalname”. Commands issued this way do not prompt for confirmation or display warning messages, and exit with non-zero status if the operation fails.
    • Accept the same principal flag names in kadmin as we do for the default_principal_flags kdc.conf variable, and vice versa. Also accept flag specifiers in the form that kadmin prints, as well as hexadecimal numbers.
    • Remove the triple-DES and RC4 encryption types from the default value of supported_enctypes, which determines the default key and salt types for new password-derived keys. By default, keys will only created only for AES128 and AES256. This mitigates some types of password guessing attacks.
    • Add support for directory names in the KRB5_CONFIG and KRB5_KDC_PROFILE environment variables.
    • Add support for authentication indicators, which are ticket annotations to indicate the strength of the initial authentication. Add support for the “require_auth” string attribute, which can be set on server principal entries to require an indicator when authenticating to the server.
    • Add support for key version numbers larger than 255 in keytab files, and for version numbers up to 65535 in KDC databases.
    • Transmit only one ETYPE-INFO and/or ETYPE-INFO2 entry from the KDC during pre-authentication, corresponding to the client’s most preferred encryption type.
    • Add support for server name identification (SNI) when proxying KDC requests over HTTPS.
    • Add support for the err_fmt profile parameter, which can be used to generate custom-formatted error messages.
  • Developer experience:
    • Change gss_acquire_cred_with_password() to acquire credentials into a private memory credential cache. Applications can use gss_store_cred() to make the resulting credentials visible to other processes.
    • Change gss_acquire_cred() and SPNEGO not to acquire credentials for IAKERB or for non-standard variants of the krb5 mechanism OID unless explicitly requested. (SPNEGO will still accept the Microsoft variant of the krb5 mechanism OID during negotiation.)
    • Change gss_accept_sec_context() not to accept tokens for IAKERB or for non-standard variants of the krb5 mechanism OID unless an acceptor credential is acquired for those mechanisms.
    • Change gss_acquire_cred() to immediately resolve credentials if the time_rec parameter is not NULL, so that a correct expiration time can be returned. Normally credential resolution is delayed until the target name is known.
    • Add krb5_prepend_error_message() and krb5_wrap_error_message() APIs, which can be used by plugin modules or applications to add prefixes to existing detailed error messages.
    • Add krb5_c_prfplus() and krb5_c_derive_prfplus() APIs, which implement the RFC 6113 PRF+ operation and key derivation using PRF+.
    • Add support for pre-authentication mechanisms which use multiple round trips, using the the KDC_ERR_MORE_PREAUTH_DATA_REQUIRED error code. Add get_cookie() and set_cookie() callbacks to the kdcpreauth interface; these callbacks can be used to save marshalled state information in an encrypted cookie for the next request.
    • Add a client_key() callback to the kdcpreauth interface to retrieve the chosen client key, corresponding to the ETYPE-INFO2 entry sent by the KDC.
    • Add an add_auth_indicator() callback to the kdcpreauth interface, allowing pre-authentication modules to assert authentication indicators.
    • Add support for the GSS_KRB5_CRED_NO_CI_FLAGS_X cred option to suppress sending the confidentiality and integrity flags in GSS initiator tokens unless they are requested by the caller. These flags control the negotiated SASL security layer for the Microsoft GSS-SPNEGO SASL mechanism.
    • Make the FILE credential cache implementation less prone to corruption issues in multi-threaded programs, especially on platforms with support for open file description locks.
  • Performance:
    • On slave KDCs, poll the master KDC immediately after processing a full resync, and do not require two full resyncs after the master KDC’s log file is reset.

Release 1.15

  • Administrator experience:
    • Add support to kadmin for remote extraction of current keys without changing them (requires a special kadmin permission that is excluded from the wildcard permission), with the exception of highly protected keys.
    • Add a lockdown_keys principal attribute to prevent retrieval of the principal’s keys (old or new) via the kadmin protocol. In newly created databases, this attribute is set on the krbtgt and kadmin principals.
    • Restore recursive dump capability for DB2 back end, so sites can more easily recover from database corruption resulting from power failure events.
    • Add DNS auto-discovery of KDC and kpasswd servers from URI records, in addition to SRV records. URI records can convey TCP and UDP servers and master KDC status in a single DNS lookup, and can also point to HTTPS proxy servers.
    • Add support for password history to the LDAP back end.
    • Add support for principal renaming to the LDAP back end.
    • Use the getrandom system call on supported Linux kernels to avoid blocking problems when getting entropy from the operating system.
  • Code quality:
    • Clean up numerous compilation warnings.
    • Remove various infrequently built modules, including some preauth modules that were not built by default.
  • Developer experience:
    • Add support for building with OpenSSL 1.1.
    • Use SHA-256 instead of MD5 for (non-cryptographic) hashing of authenticators in the replay cache. This helps sites that must build with FIPS 140 conformant libraries that lack MD5.
  • Protocol evolution:
    • Add support for the AES-SHA2 enctypes, which allows sites to conform to Suite B crypto requirements.

Release 1.16

  • Administrator experience:
    • The KDC can match PKINIT client certificates against the “pkinit_cert_match” string attribute on the client principal entry, using the same syntax as the existing “pkinit_cert_match” profile option.
    • The ktutil addent command supports the “-k 0” option to ignore the key version, and the “-s” option to use a non-default salt string.
    • kpropd supports a –pid-file option to write a pid file at startup, when it is run in standalone mode.
    • The “encrypted_challenge_indicator” realm option can be used to attach an authentication indicator to tickets obtained using FAST encrypted challenge pre-authentication.
    • Localization support can be disabled at build time with the –disable-nls configure option.
  • Developer experience:
    • The kdcpolicy pluggable interface allows modules control whether tickets are issued by the KDC.
    • The kadm5_auth pluggable interface allows modules to control whether kadmind grants access to a kadmin request.
    • The certauth pluggable interface allows modules to control which PKINIT client certificates can authenticate to which client principals.
    • KDB modules can use the client and KDC interface IP addresses to determine whether to allow an AS request.
    • GSS applications can query the bit strength of a krb5 GSS context using the GSS_C_SEC_CONTEXT_SASL_SSF OID with gss_inquire_sec_context_by_oid().
    • GSS applications can query the impersonator name of a krb5 GSS credential using the GSS_KRB5_GET_CRED_IMPERSONATOR OID with gss_inquire_cred_by_oid().
    • kdcpreauth modules can query the KDC for the canonicalized requested client principal name, or match a principal name against the requested client principal name with canonicalization.
  • Protocol evolution:
    • The client library will continue to try pre-authentication mechanisms after most failure conditions.
    • The KDC will issue trivially renewable tickets (where the renewable lifetime is equal to or less than the ticket lifetime) if requested by the client, to be friendlier to scripts.
    • The client library will use a random nonce for TGS requests instead of the current system time.
    • For the RC4 string-to-key or PAC operations, UTF-16 is supported (previously only UCS-2 was supported).
    • When matching PKINIT client certificates, UPN SANs will be matched correctly as UPNs, with canonicalization.
  • User experience:
    • Dates after the year 2038 are accepted (provided that the platform time facilities support them), through the year 2106.
    • Automatic credential cache selection based on the client realm will take into account the fallback realm and the service hostname.
    • Referral and alternate cross-realm TGTs will not be cached, avoiding some scenarios where they can be added to the credential cache multiple times.
    • A German translation has been added.
  • Code quality:
    • The build is warning-clean under clang with the configured warning options.
    • The automated test suite runs cleanly under AddressSanitizer.

Pre-authentication mechanisms