CMS_SIGNED_GET_ATTR(3SSL)

📦

version 4.0.3 · 12 versions

👑 CMS_SIGNED_GET_ATTR — the OpenSSL `3SSL` page, but make it cute ✨

okay so bestie. listen. you're reading CMS_SIGNED_GET_ATTR(3SSL) and honestly? it's giving "the attribute manager for CMS SignerInfos." no cap. 🎀

🌸 NAME 🌸

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 — aka the CMS signed and unsigned attribute functions 💅

✨ SYNOPSIS ✨

like, here's the whole vibe, verbatim, don't touch it:

#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 🦋

so. CMS_signerInfo (bestie, write it how the page writes it, iykyk) keeps separate attribute lists for signed and unsigned attributes. every CMS_signed_XXX() function is for the signed side, and every CMS_unsigned_XXX() function is for the unsigned side. and here's the slay part: because the CMS_unsigned_XXX() functions literally work the same way as their CMS_signed_XXX() equivalents, only the CMS_signed_XXX() ones get described below. equality. 💅

Let's go one by one, bestie:

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 guess what — you can use it on the next call to CMS_signed_get_attr_by_OBJ() as the value of lastpos to iterate through the remaining attributes. and on the very first call? set lastpos to any negative value and it starts searching from the start of the signed attribute list. iconic iterator behaviour, no notes. 🔥
CMS_signed_get_attr_by_NID() — same energy as CMS_signed_get_attr_by_OBJ() except 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. whole assembly line moment. 🧚
CMS_signed_add1_attr_by_NID() — same as CMS_signed_add1_attr_by_OBJ() except 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() — same as CMS_signed_add1_attr_by_OBJ() except 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 obj, starting at index lastpos, and returns the data retrieved from the found attribute's first ASN1_TYPE object. an error will occur if:
- the attribute type type does not match the type of the ASN1_TYPE object, OR
- type is either V_ASN1_BOOLEAN or V_ASN1_NULL, OR
- the attribute is not found.

and bestie, more conditions: if lastpos is less than -1 then an error will occur if there are multiple objects in the signed attribute list that match obj. and 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. read those twice, fr fr. 😭

refer to X509_ATTRIBUTE(3) for information related to attributes. 🫶

💜 RETURN VALUES 💜

the CMS_unsigned_XXX() functions return values are similar to those of the equivalent CMS_signed_XXX() functions. twin behaviour. 👑
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 a 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. yes queen, binary.
CMS_signed_get0_data_by_OBJ() — returns the data retrieved from the found signed attribute's first ASN1_TYPE object, or NULL if an error occurs.

🌈 NOTES 🌈

some attributes are added automatically during the signing process. like, you didn't even ask. 💅

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. package deal, periodt.
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, bestie, pay attention 🚨:

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

and now the important bit, so don't scroll past it: 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 — they're 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().

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>.

okay that's the whole thing bestie, you ate that 💖 version 4.0.3, dated 2026-09-29, and yeah the page is literally called CMS_SIGNED_GET_ATTR(3SSL) — go forth and manage your attributes, main character energy only, mwah 💅✨🌙

📦 where this page comes from

ubuntu stonking: libssl-doc 4.0.3-1ubuntu1 · Apache-2.0
💖 girlified by deepseek-ai/DeepSeek-V4.1-Flash on 2026-11-03: a language model's rewrite of the original, under its terms