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David5D15
Participant
March 18, 2021
Question

Adobe Acrobat Reader DC PKCS#11 ECC - unsupported algorithm error

  • March 18, 2021
  • 3 replies
  • 9826 views

Hello, we tried to generate a digital signature with PKCS#11:

  • Adobe Acrobat Reader DC version 2021.001.20145
  • Default signing format: PKCS#7 - Detached
  • PKCS#11 key stored on smart card (QSCD):
    CKA_KEY_TYPE: CKK_EC
    CKA_EC_PARAMS: { 1 2 840 10045 3 1 7 }
  • ECDSA elliptic curve P256 with digest algorithm SHA256
  • Windows 10, macOS Catalina

We successfully loaded the PKCS#11 module. We started the signature process, added the PIN and after we tried to save the document we received the following error message:
"Error encountered while signing: unsupported algorithm."

The last function is called by Acrobat is the C_GetAttributeValue with CKA_KEY_TYPE: CKK_EC. There is further communication between Acrobat and PKCS#11 module.
According to the Acrobat DC Digital Signatures guide, the above-mentioned algorithm is supported:
https://www.adobe.com/devnet-docs/acrobatetk/tools/DigSigDC/standards.html
On the other hand, with Minidriver, we can generate a digital signature with the same key/certificate.

Is there any information about PKCS#11 supported algorithms?

Thanks

 

    3 replies

    patrik.akd
    patrik.akd
    Participant
    March 27, 2026

    I can confirm the same issue. After extended PKCS#11 library debugging we’ve come to a conclusion that as soon as key has type CKK_EC (or deprecated CKK_ECDSA) Adobe fails with “Unsupported Algorithm”.

     

    So from my understanding it is not even an algorithm issue but Adobe does not support CKK_EC key type at all while using PKCS#11 libraries.

     

    There is no way to resolve this if using PKCS#11, it is an unsupported key type which Adobe should implement.

    Meenakshi0101
    Community Manager
    Meenakshi0101Community Manager
    Community Manager
    March 30, 2026

    Hi patrik.akd,

     

     

    Thank you for reaching out and bringing this behaviour to our attention.

     

    We need to investigate this further with our team. Could you please confirm whether this issue occurs only when using the key type CKK_EC (or the deprecated CKK_ECDSA)? We will determine whether it is unsupported or whether another issue is causing this error.

     

    It would also be helpful if you could provide a short video demonstrating the steps you took. Additionally, please share the current versions of Acrobat and your operating system on the machine.

     

    Let us know if you need any help.

     

    Thanks,

    Meenakshi

     

    patrik.akd
    patrik.akd
    Participant
    March 30, 2026

    Hi ​@Meenakshi0101,

     

    Yes I can confirm we have observed this issue only when using the key type CKK_EC. When using an object with CKK_RSA key type there is no such issue. We do not issue cards with other types of keys so I can not say for the rest.

     

    After debugging our PKCS#11 library we have concluded that Adobe returns “Unsupported Algorithm” message after calling C_GetAttributeValue for CKA_KEY_TYPE which returns value CKK_EC.

     

    Here is a short video: https://col.certilia.com/services/files/public/link/download/fmUJpqhjWWlcbiqgnnwyune2iYDW0gmjyANkuMBP7I7LTYYf9k

     

    I’ve observed this on both Windows and macOS. Adobe version in video is 2026.001.21346 (macOS). I do not have a Windows machine at hand at the moment to do a second check but I believe this is not a platform specific issue.

     

    Regards,

    Patrik

     

     

     

     

    K
    Koen225142565mmt
    Participant
    January 5, 2022

    Did you solved this problem. We have now the same problem. I have a new eID. But the certificates were not longer recognised. So I re-Installed Adobe Acrobat Reader DC. The certificate for signature is now accepted and tested (5 green check marks). But at the end of the process to sign a .pdf document the error appears: (dutch:) “Fout aangetroffen tijdens ondertekenen: Niet-ondersteund algoritme” (free translated:)”Error encountered while signing: Unsupported algorithm”. What can I do? Please answer.

    K
    Koen225142565mmt
    Participant
    February 1, 2022

    The problem is solved. Solution : configure Acrobat Reader without pkcs#11 module.
    If this module has already been linked, the already linked module must therefore be uncoupled again.
    After unlinking, restart Acrobat Reader and try signing again.
    BELGIUM uses software called eID middleware that communicates with the card for Windows. In the past Acrobat Reader could not use this middleware and Acrobat Reader needed the pkcs11 module to do the communication with the card. Recently, ADOBE has made the necessary changes so that READER can work with the middleware.
    The pkcs11 module has now basically become optional within Acrobat Reader.

      D
      Denis5E48
      Participant
      August 19, 2022

      Hi Koen, 

      THanks for the help. Could you explain further how to set up the eid for acrobat since "ADOBE has made the necessary changes so that READER can work with the middleware." ? 

      If it is not with the pkcs#11 anymore, how should I configure the card reader to work with Acrobat for digital signatures? 

        A
        arnauldd23274658
        Participant
        June 1, 2021

        Hello,

        Is there any update on this problem please ?

        Is this really supposed to be supported ?

         

        Thanks all,

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