Cryptography and SSL/TLS Toolkit



OSSL_CMP_exec_certreq, OSSL_CMP_exec_IR_ses, OSSL_CMP_exec_CR_ses, OSSL_CMP_exec_P10CR_ses, OSSL_CMP_exec_KUR_ses, OSSL_CMP_IR, OSSL_CMP_CR, OSSL_CMP_P10CR, OSSL_CMP_KUR, OSSL_CMP_try_certreq, OSSL_CMP_exec_RR_ses, OSSL_CMP_exec_GENM_ses - functions implementing CMP client transactions


#include <openssl/cmp.h>

X509 *OSSL_CMP_exec_certreq(OSSL_CMP_CTX *ctx, int req_type,
                            const OSSL_CRMF_MSG *crm);
X509 *OSSL_CMP_exec_IR_ses(OSSL_CMP_CTX *ctx);
X509 *OSSL_CMP_exec_CR_ses(OSSL_CMP_CTX *ctx);
X509 *OSSL_CMP_exec_P10CR_ses(OSSL_CMP_CTX *ctx);
X509 *OSSL_CMP_exec_KUR_ses(OSSL_CMP_CTX *ctx);
#define OSSL_CMP_IR
#define OSSL_CMP_CR
#define OSSL_CMP_P10CR
#define OSSL_CMP_KUR
int OSSL_CMP_try_certreq(OSSL_CMP_CTX *ctx, int req_type,
                         const OSSL_CRMF_MSG *crm, int *checkAfter);
int OSSL_CMP_exec_RR_ses(OSSL_CMP_CTX *ctx);


This is the OpenSSL API for doing CMP (Certificate Management Protocol) client-server transactions, i.e., sequences of CMP requests and responses.

All functions take a populated OSSL_CMP_CTX structure as their first argument. Usually the server name, port, and path ("CMP alias") need to be set, as well as credentials the client can use for authenticating itself to the server. In order to authenticate the server the client typically needs a trust store. The functions return their respective main results directly, while there are also accessor functions for retrieving various results and status information from the ctx. See OSSL_CMP_CTX_new(3) etc. for details.

The default conveying protocol is HTTP. Timeout values may be given per request-response pair and per transaction. See OSSL_CMP_MSG_http_perform(3) for details.

OSSL_CMP_exec_IR_ses() requests an initial certificate from the given PKI.

OSSL_CMP_exec_CR_ses() requests an additional certificate.

OSSL_CMP_exec_P10CR_ses() conveys a legacy PKCS#10 CSR requesting a certificate.

OSSL_CMP_exec_KUR_ses() obtains an updated certificate.

These four types of certificate enrollment are implemented as macros calling OSSL_CMP_exec_certreq().

OSSL_CMP_exec_certreq() performs a certificate request of the type specified by the req_type parameter, which may be IR, CR, P10CR, or KUR. For IR, CR, and KUR, the certificate template to be used in the request may be supplied via the crm parameter pointing to a CRMF structure. Typically crm is NULL, then the template ingredients are taken from ctx and need to be filled in using OSSL_CMP_CTX_set1_subjectName(3), OSSL_CMP_CTX_set0_newPkey(3), OSSL_CMP_CTX_set1_oldCert(3), etc. For P10CR, OSSL_CMP_CTX_set1_p10CSR(3) needs to be used instead. The enrollment session may be blocked by sleeping until the addressed CA (or an intermediate PKI component) can fully process and answer the request.

OSSL_CMP_try_certreq() is an alternative to the above functions that is more flexible regarding what to do after receiving a checkAfter value. When called for the first time (with no certificate request in progress for the given ctx) it starts a new transaction by sending a certificate request constructed as stated above using the req_type and optional crm parameter. Otherwise (when according to ctx a 'waiting' status has been received before) it continues polling for the pending request unless the req_type argument is < 0, which aborts the request. If the requested certificate is available the function returns 1 and the caller can use OSSL_CMP_CTX_get0_newCert(3) to retrieve the new certificate. If no error occurred but no certificate is available yet then OSSL_CMP_try_certreq() remembers in the CMP context that it should be retried and returns -1 after assigning the received checkAfter value via the output pointer argument (unless it is NULL). The checkAfter value indicates the number of seconds the caller should let pass before trying again. The caller is free to sleep for the given number of seconds or for some other time and/or to do anything else before retrying by calling OSSL_CMP_try_certreq() again with the same parameter values as before. OSSL_CMP_try_certreq() then polls to see whether meanwhile the requested certificate is available. If the caller decides to abort the pending certificate request and provides a negative value as the req_type argument then OSSL_CMP_try_certreq() aborts the CMP transaction by sending an error message to the server.

OSSL_CMP_exec_RR_ses() requests the revocation of the certificate specified in the ctx using OSSL_CMP_CTX_set1_oldCert(3). RFC 4210 is vague in which PKIStatus should be returned by the server. We take "accepted" and "grantedWithMods" as clear success and handle "revocationWarning" and "revocationNotification" just as warnings because CAs typically return them as an indication that the certificate was already revoked. "rejection" is a clear error. The values "waiting" and "keyUpdateWarning" make no sense for revocation and thus are treated as an error as well.

OSSL_CMP_exec_GENM_ses() sends a general message containing the sequence of infoType and infoValue pairs (InfoTypeAndValue; short: ITAV) optionally provided in the ctx using OSSL_CMP_CTX_push0_genm_ITAV(3). On success it records in ctx the status OSSL_CMP_PKISTATUS_accepted and returns the list of ITAVs received in the GENP message. This can be used, for instance, to poll for CRLs or CA Key Updates. See RFC 4210 section 5.3.19 and appendix E.5 for details.


CMP is defined in RFC 4210 (and CRMF in RFC 4211).

The CMP client implementation is limited to one request per CMP message (and consequently to at most one response component per CMP message).

When a client obtains from a CMP server CA certificates that it is going to trust, for instance via the caPubs field of a certificate response, authentication of the CMP server is particularly critical. So special care must be taken setting up server authentication in ctx using functions such as OSSL_CMP_CTX_set0_trustedStore(3) (for certificate-based authentication) or OSSL_CMP_CTX_set1_secretValue(3) (for MAC-based protection).


OSSL_CMP_exec_certreq(), OSSL_CMP_exec_IR_ses(), OSSL_CMP_exec_CR_ses(), OSSL_CMP_exec_P10CR_ses(), and OSSL_CMP_exec_KUR_ses() return a pointer to the newly obtained X509 certificate on success, NULL on error. This pointer will be freed implicitly by OSSL_CMP_CTX_free() or CSSL_CMP_CTX_reinit().

OSSL_CMP_try_certreq() returns 1 if the requested certificate is available via OSSL_CMP_CTX_get0_newCert(3) or on successfully aborting a pending certificate request, 0 on error, and -1 in case a 'waiting' status has been received and checkAfter value is available. In the latter case OSSL_CMP_CTX_get0_newCert(3) yields NULL and the output parameter checkAfter has been used to assign the received value unless checkAfter is NULL.

OSSL_CMP_exec_RR_ses() returns 1 on success, 0 on error.

OSSL_CMP_exec_GENM_ses() returns NULL on error, otherwise a pointer to the sequence of ITAV received, which may be empty. This pointer must be freed by the caller.


See OSSL_CMP_CTX for examples on how to prepare the context for these functions.


OSSL_CMP_CTX_new(3), OSSL_CMP_CTX_free(3), OSSL_CMP_CTX_set1_subjectName(3), OSSL_CMP_CTX_set0_newPkey(3), OSSL_CMP_CTX_set1_p10CSR(3), OSSL_CMP_CTX_set1_oldCert(3), OSSL_CMP_CTX_get0_newCert(3), OSSL_CMP_CTX_push0_genm_ITAV(3), OSSL_CMP_MSG_http_perform(3)


The OpenSSL CMP support was added in OpenSSL 3.0.

Copyright 2007-2023 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (the "License"). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at