MIT kerberos failed to decrypt KRB_AP_REQ with error KRB5KRB_AP_ERR_BAD_INTEGRITY

[Ashi1986]

Hi sir,

While using the encryption type RC4-HMAC-NT, AES128-SHA1 or AES256-SHA1
connection to the principal is failed due to KRB_AP_REQ cannot be decrypted
by the MIT kerberos 1.13.2.
After configuring the DES-BSC-CRC and DES-CBC-MD5 encryption type, from the
client machine connection to the principal becomes successful.

Setup is as follows:

1. Set up AD DC on windows server 2012 R2

2. Created a domain user and checked the corresponding option in case of
AES128-SHA1 "This account supports Kerberos AES 128 bit encryption" and "do
not require Kerberos pre authentication".

3. On the windows server 2012 R2, in local Policies->Security Options
->"Network Security: configure encryption type allowed for Kerberos"
AES_128_HMAC_SHA1 and AES_256_HMAC_SHA1 is selected

4. On windows 2012 R2, by using ADSIEDIT.msc, value of 
msDS-SupportedEncryptionTypesis set to 28.

5. On the windows client machine [windows 8.1] which is in same domain, in
local Policies->Security Options ->"Network Security: configure encryption
type allowed for Kerberos" AES_128_HMAC_SHA1  and AES_256_HMAC_SHA1 is
selected.

6. Created keytab file on windows 2012 Server R2 by using the KTPASS command
[corresponding encryption type is used with -crypto option]

ktpass -princ host/<host name>@domain name -mapuser <domain user name> -pass
<passwd of domain user> -crypto AES128-SHA1 -ptype KRB5_NT_PRINCIPAL -out
C:\KeyTab\Test4AES-128-U6.keytab
and KTPASS executed successfully.

7. login in the windows machine [windows 8.1] with the domain user as used
in KTPASS command and trying to access the  resource as configured as
principal in KTPASS command.

[Analysis]
1. while debugging the MIT kerberos sources [1.13.2] it is identified that
in case of RC4-HMAC-NT encryption type while decryption function
krb5int_arcfour_decrypt returns with KRB5KRB_AP_ERR_BAD_INTEGRITY.

2. similarly in case of encryption type AES128-SHA1 and AES256-SHA1, it
fails in fails in decryption with error KRB5KRB_AP_ERR_BAD_INTEGRITY.

3. from the debugger it is confirmed that encryption type and KVno is
correctly configured and correctly displayed in the debugger.

4. From the wire shark network analyzer it is identified that in case of
DES-CBC-MD5 encryption type length of the KRB_AP_REQ is 1808 bytes [which is
dividable by block size (8 bytes) of DES-CBC-MD5] and in case of DES-CBC-MD5
connection becomes successful.

5. When RC4-HMAC-NT or AES128-SHA1 is configured then length of KRB_AP_REQ
is 1813 and 1784 respectively and both are not be dividable by their block
size and in these scenarios server failed to decrypt the KRB_AP_REQ.

[Request]
Please suggest settings/viewpoints to resolve the above mentioned problem.

Thank You



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