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Why are CIFS sessions not signed when encryption and SMB signing are both enabled on the SVM?

  1. Last updated
    Feb 28, 2025
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Category:
ontap-9
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nas
Last Updated:
2/28/2025, 9:04:07 AM

Applies to

  • ONTAP 9
  • CIFS
  • SMB Signing
  • SMB Encryption

Answer

  • If a CIFS session is marked for both Signing and Encryption then SMB Encryption supersedes SMB signing
    • Microsoft discusses this particular interaction in the following passage on SMB Security Enhancements:
      • "SMB Encryption uses the Advanced Encryption Standard (AES)-GCM and CCM algorithm to encrypt and decrypt the data. AES-CMAC and AES-GMAC also provide data integrity validation (signing) for encrypted file shares, regardless of the SMB signing settings."
  • Because SMB encryption is a higher level of message security that also preserves integrity, SMB signing is not utilized on encrypted sessions

Example:

Cluster01::> vserver cifs security show -vserver SVM1 -fields is-signing-required,is-smb-encryption-required
vserver     is-signing-required is-smb-encryption-required
----------- ------------------- --------------------------
SVM1        true                true

Cluster01::> vserver cifs session show -vserver SVM1 -fields is-session-signed,smb-encryption-status
node         vserver    session-id          connection-id is-session-signed smb-encryption-status
------------ ---------- ------------------- ------------- ----------------- ---------------------
Cluster01-02 SVM1         5783747821497729909 952531972     false             encrypted
Cluster01-02 SVM1         5783747821497731202 952532894     false             encrypted
Cluster01-02 SVM1         5783747821497731343 952532985     false             encrypted
3 entries were displayed.

  • You may still see signing implemented with partially encrypted sessions if the encryption is enforced at the share-level rather than the server-level

Example:

Cluster01::> vserver cifs security show -vserver SVM1 -fields is-signing-required,is-smb-encryption-required
vserver     is-signing-required is-smb-encryption-required
----------- ------------------- --------------------------
SVM1        true                false

Cluster01::> cifs share show -vserver SVM1 -share-name encrypted_share -fields share-properties
vserver  share-name          share-properties
-------- ------------------- -----------------
SVM1     encrypted_share     encrypt-data

Cluster01::> vserver cifs session show -vserver SVM1 -fields is-session-signed,smb-encryption-status,share-names
node         vserver session-id          connection-id is-session-signed smb-encryption-status share-names
------------ ------- ------------------- ------------- ----------------- --------------------- -----------
Cluster01-02 SVM1    5783747821497729909 952531972     true              partially-encrypted   encrypted_share

Additional Information

N/A

 

 

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