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This article includes updates for Nexus OCSP Responder 6.2.6.

This article provides installation requirements and interoperability data for Nexus OCSP Responder.


CPUQuad Core 2.4 GHz
Disk size

20 GB

Memory4 GB RAM


64-bit PKCS#11-driver

Nexus OCSP Responder scales well with a server of multiple cores. More memory can be required when many logical responders are hosted in a single server instance and large CRLs are loaded by the responder. For load tests, also consider the HSM performance to not introduce a bottle-neck. Performance is affected by the Nexus OCSP Responder signing key length.

The following operating systems are supported:

  • CentOS 7
  • Rocky Linux 9
  • Red Hat Enterprise Linux 7, 8, 9
  • SUSE Linux Enterprise Server 15
  • OpenSUSE Leap 15
  • Microsoft Windows 2012 Server
  • Microsoft Windows 2016 Server
  • Microsoft Windows 2019 Server

The following software is supported:

  • 64-bit Java Runtime Environment (JRE) version 17.
  • Nexus OCSP Responder is compatible with both OpenJDK and Oracle Java.

It is important that all participants in a PKI use the same time standard. Specifically Nexus OCSP Responder has to agree on the time with the CAs issuing CRLs/CILs and with the OCSP clients.

Make sure these clocks are synchronized, that is, the participants are using a synchronization protocol such as Network Time Protocol, NTP.


A PKCS#11 compliant device can be used for handling of CA key pairs, system keys, protection of archived keys, and for key generation.

For functional specifications, known issues and limitations related to current PKCS#11 drivers, see each HSM vendor’s web site. 

The following devices are explicitly verified for Certificate Manager and for Nexus OCSP Responder:

  • AEP Systems Sureware Keyper, FIPS 140-1 level 4
  • Atos Bull Trustway Proteccio NetHSM

  • DocuSign ARX PrivateServer
  • Gemalto SafeNet ProtectServer Internal - Express 2
  • Gemalto SafeNet ProtectServer External 2
  • Thales Luna CA3, FIPS 140-1 lvl 3
  • Thales Luna CA4, FIPS 140-2 lvl 3
  • Thales Luna SA 4.4, FIPS 140-2 lvl 3
  • Thales Luna SA 5.0, FIPS 140-2 lvl 3
  • Thales Luna G5
  • Thales Luna HSM 6

  • Thales Luna Network HSM 7
  • Thales Luna PCIe HSM 7
  • IBM 4758, FIPS 140-1 level 3 and 4
  • Nitrokey HSM 2
  • Entrust nShield Connect+, FIPS 140-2 level 3
  • Entrust nShield Solo+, FIPS 140-2 level 3
  • Entrust nShield Edge
  • Utimaco CryptoServer Security Server CS 10/50 LAN/PCI, FIPS 140-2 level 3 (level 4 for physical)
  • Utimaco CryptoServer Security Server Se 12/52/420/1200 LAN/PCI, FIPS 140-2 level 3
  • Yubico YubiHSM 2

PIN decryption is not allowed using a FIPS mode HSM.

The following key types and corresponding signature algorithms in certificate, CA, CRL, CIL, and responder certificate are supported:

Key types

  • RSA
  • EC
  • Edward


  • SHA-1
  • SHA-2