CMS_SIGNED_GET_ATTR(3ossl)

📦 version 15.1, in freebsd 15.1

💖 NAME 💖

okay bestie, this is the manual page for CMS_SIGNED_GET_ATTR(3ossl) — OpenSSL’s guide to CMS signed and unsigned attribute functions 🎀. The whole function squad on this page is:

CMS_signed_get_attr_count
CMS_signed_get_attr_by_NID
CMS_signed_get_attr_by_OBJ
CMS_signed_get_attr
CMS_signed_delete_attr
CMS_signed_add1_attr
CMS_signed_add1_attr_by_OBJ
CMS_signed_add1_attr_by_NID
CMS_signed_add1_attr_by_txt
CMS_signed_get0_data_by_OBJ
CMS_unsigned_get_attr_count
CMS_unsigned_get_attr_by_NID
CMS_unsigned_get_attr_by_OBJ
CMS_unsigned_get_attr
CMS_unsigned_delete_attr
CMS_unsigned_add1_attr
CMS_unsigned_add1_attr_by_OBJ
CMS_unsigned_add1_attr_by_NID
CMS_unsigned_add1_attr_by_txt
CMS_unsigned_get0_data_by_OBJ

✨ SYNOPSIS ✨

the exact signatures, no cap:

        #include <openssl/cms.h>

        int CMS_signed_get_attr_count(const CMS_SignerInfo *si);
        int CMS_signed_get_attr_by_NID(const CMS_SignerInfo *si, int nid,
                                       int lastpos);
        int CMS_signed_get_attr_by_OBJ(const CMS_SignerInfo *si, const ASN1_OBJECT *obj,
                                       int lastpos);
        X509_ATTRIBUTE *CMS_signed_get_attr(const CMS_SignerInfo *si, int loc);
        X509_ATTRIBUTE *CMS_signed_delete_attr(CMS_SignerInfo *si, int loc);
        int CMS_signed_add1_attr(CMS_SignerInfo *si, X509_ATTRIBUTE *attr);
        int CMS_signed_add1_attr_by_OBJ(CMS_SignerInfo *si,
                                        const ASN1_OBJECT *obj, int type,
                                        const void *bytes, int len);
        int CMS_signed_add1_attr_by_NID(CMS_SignerInfo *si,
                                        int nid, int type,
                                        const void *bytes, int len);
        int CMS_signed_add1_attr_by_txt(CMS_SignerInfo *si,
                                        const char *attrname, int type,
                                        const void *bytes, int len);
        void *CMS_signed_get0_data_by_OBJ(const CMS_SignerInfo *si,
                                          const ASN1_OBJECT *oid,
                                          int lastpos, int type);

        int CMS_unsigned_get_attr_count(const CMS_SignerInfo *si);
        int CMS_unsigned_get_attr_by_NID(const CMS_SignerInfo *si, int nid,
                                         int lastpos);
        int CMS_unsigned_get_attr_by_OBJ(const CMS_SignerInfo *si,
                                         const ASN1_OBJECT *obj, int lastpos);
        X509_ATTRIBUTE *CMS_unsigned_get_attr(const CMS_SignerInfo *si, int loc);
        X509_ATTRIBUTE *CMS_unsigned_delete_attr(CMS_SignerInfo *si, int loc);
        int CMS_unsigned_add1_attr(CMS_SignerInfo *si, X509_ATTRIBUTE *attr);
        int CMS_unsigned_add1_attr_by_OBJ(CMS_SignerInfo *si,
                                          const ASN1_OBJECT *obj, int type,
                                          const void *bytes, int len);
        int CMS_unsigned_add1_attr_by_NID(CMS_SignerInfo *si,
                                          int nid, int type,
                                          const void *bytes, int len);
        int CMS_unsigned_add1_attr_by_txt(CMS_SignerInfo *si,
                                          const char *attrname, int type,
                                          const void *bytes, int len);
        void *CMS_unsigned_get0_data_by_OBJ(CMS_SignerInfo *si, ASN1_OBJECT *oid,
                                            int lastpos, int type);

🌸 DESCRIPTION 🌸

okay so CMS_signerInfo contains separate attribute lists for signed and unsigned attributes. Each CMS_signed_XXX() function is used for signed attributes, and each CMS_unsigned_XXX() function is used for unsigned attributes. Since the CMS_unsigned_XXX() functions work in the same way as the CMS_signed_XXX() equivalents, only the CMS_signed_XXX() functions are described below. periodt 💅

CMS_signed_get_attr_by_OBJ() — finds the location of the first matching object obj in the SignerInfo’s si signed attribute list. The search starts at the position after lastpos. If the returned value is positive then it can be used on the next call to CMS_signed_get_attr_by_OBJ() as the value of lastpos in order to iterate through the remaining attributes. lastpos can be set to any negative value on the first call, in order to start searching from the start of the signed attribute list.

CMS_signed_get_attr_by_NID() — similar to CMS_signed_get_attr_by_OBJ() except that it passes the numerical identifier (NID) nid associated with the object. See <openssl/obj_mac.h> for a list of NID_*.

CMS_signed_get_attr() — returns the X509_ATTRIBUTE object at index loc in the si signed attribute list. loc should be in the range from 0 to CMS_signed_get_attr_count() - 1.

CMS_signed_delete_attr() — removes the X509_ATTRIBUTE object at index loc in the si signed attribute list. An error occurs if the si attribute list is NULL.

CMS_signed_add1_attr() — pushes a copy of the passed in X509_ATTRIBUTE object to the si signed attribute list. A new signed attribute list is created if required. An error occurs if attr is NULL.

CMS_signed_add1_attr_by_OBJ() — creates a new signed X509_ATTRIBUTE using X509_ATTRIBUTE_set1_object() and X509_ATTRIBUTE_set1_data() to assign a new obj with type type and data bytes of length len and then pushes it to the key object's attribute list.

CMS_signed_add1_attr_by_NID() — similar to CMS_signed_add1_attr_by_OBJ() except that it passes the numerical identifier (NID) nid associated with the object. See <openssl/obj_mac.h> for a list of NID_*.

CMS_signed_add1_attr_by_txt() — similar to CMS_signed_add1_attr_by_OBJ() except that it passes a name attrname associated with the object. See <openssl/obj_mac.h> for a list of SN_* names.

CMS_signed_get0_data_by_OBJ() — finds the first attribute in a si signed attributes list that matches the obj starting at index lastpos and returns the data retrieved from the found attributes first ASN1_TYPE object. An error will occur if the attribute type type does not match the type of the ASN1_TYPE object OR if type is either V_ASN1_BOOLEAN or V_ASN1_NULL OR the attribute is not found. If lastpos is less than -1 then an error will occur if there are multiple objects in the signed attribute list that match obj. If lastpos is less than -2 then an error will occur if there is more than one ASN1_TYPE object in the found signed attribute.

Refer to X509_ATTRIBUTE(3) for information related to attributes. iykyk 🦋

🦋 RETURN VALUES 🦋

The CMS_unsigned_XXX() functions return values are similar to those of the equivalent CMS_signed_XXX() functions.

CMS_signed_get_attr_count() — returns the number of signed attributes in the SignerInfo si, or -1 if the signed attribute list is NULL.
CMS_signed_get_attr_by_OBJ() — returns -1 if either the signed attribute list of si is empty OR if obj is not found, otherwise it returns the location of the obj in the SignerInfo’s si signed attribute list.
CMS_signed_get_attr_by_NID() — similar to CMS_signed_get_attr_by_OBJ() except that it returns -2 if the nid is not known by OpenSSL.
CMS_signed_get_attr() — returns either a signed X509_ATTRIBUTE or NULL on error.
CMS_signed_delete_attr() — returns either the removed signed X509_ATTRIBUTE or NULL if there is an error.
CMS_signed_add1_attr(), CMS_signed_add1_attr_by_OBJ(), CMS_signed_add1_attr_by_NID(), CMS_signed_add1_attr_by_txt() — return 1 on success or 0 on error.
CMS_signed_get0_data_by_OBJ() — returns the data retrieved from the found signed attributes first ASN1_TYPE object, or NULL if an error occurs.

🧚 NOTES 🧚

Some attributes are added automatically during the signing process. lowkey important 👀

Calling CMS_SignerInfo_sign() adds the NID_pkcs9_signingTime signed attribute.
Calling CMS_final(), CMS_final_digest() or CMS_dataFinal() adds the NID_pkcs9_messageDigest signed attribute.
The NID_pkcs9_contentType signed attribute is always added if the NID_pkcs9_signingTime attribute is added.
Calling CMS_sign_ex(), CMS_sign_receipt() or CMS_add1_signer() may add attributes depending on the flags parameter. See CMS_add1_signer(3) for more information.

OpenSSL applies special rules for the following attribute NIDs:

CMS Signed Attributes: NID_pkcs9_contentType NID_pkcs9_messageDigest NID_pkcs9_signingTime
ESS Signed Attributes: NID_id_smime_aa_signingCertificate NID_id_smime_aa_signingCertificateV2 NID_id_smime_aa_receiptRequest
CMS Unsigned Attributes: NID_pkcs9_countersignature

CMS_signed_add1_attr(), CMS_signed_add1_attr_by_OBJ(), CMS_signed_add1_attr_by_NID(), CMS_signed_add1_attr_by_txt() and the equivalent CMS_unsigned_add1_attrXXX() functions allow duplicate attributes to be added. The attribute rules are not checked during these function calls, and are deferred until the sign or verify process (i.e. during calls to any of CMS_sign_ex(), CMS_sign(), CMS_sign_receipt(), CMS_add1_signer(), CMS_Final(), CMS_dataFinal(), CMS_final_digest(), CMS_verify(), CMS_verify_receipt() or CMS_SignedData_verify()).

bestie, yes: duplicates are allowed here, and the rule-checking is deferred to sign/verify time. the way that works 💀

For CMS attribute rules see RFC 5652 Section 11. For ESS attribute rules see RFC 2634 Section 1.3.4 and RFC 5035 Section 5.4.

💜 SEE ALSO 💜

X509_ATTRIBUTE(3)

👑 COPYRIGHT 👑

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 <https://www.openssl.org/source/license.html>.

xoxo bestie 💅 this page is from OpenSSL 3.5.6, dated 2026-04-07, and it’s literally CMS_SIGNED_GET_ATTR(3ossl) — now go slay those attributes ✨🫶

📦 where this page comes from

freebsd 15.1: base 15.1
💖 girlified by deepseek-ai/DeepSeek-V4.1-Flash-1017 on 2026-11-04: a language model's rewrite of the original, under its terms