SMIME_read_CMS.3ossl - Man Page

parse S/MIME message


 #include <openssl/cms.h>

 CMS_ContentInfo *SMIME_read_CMS_ex(BIO *bio, int flags, BIO **bcont,
                                    CMS_ContentInfo **cms);
 CMS_ContentInfo *SMIME_read_CMS(BIO *in, BIO **bcont);


SMIME_read_CMS() parses a message in S/MIME format.

in is a BIO to read the message from.

If cleartext signing is used then the content is saved in a memory bio which is written to *bcont, otherwise *bcont is set to NULL.

The parsed CMS_ContentInfo structure is returned or NULL if an error occurred.

SMIME_read_CMS_ex() is similar to SMIME_read_CMS() but optionally a previously created cms CMS_ContentInfo object can be supplied as well as some flags. To create a cms object use CMS_ContentInfo_new_ex(3). If the flags argument contains CMS_BINARY then the input is assumed to be in binary format and is not translated to canonical form. If in addition SMIME_ASCIICRLF is set then the binary input is assumed to be followed by CR and LF characters, else only by an LF character. If flags is 0 and cms is NULL then it is identical to SMIME_read_CMS().


If *bcont is not NULL then the message is clear text signed. *bcont can then be passed to CMS_verify() with the CMS_DETACHED flag set.

Otherwise the type of the returned structure can be determined using CMS_get0_type().

To support future functionality if bcont is not NULL *bcont should be initialized to NULL. For example:

 BIO *cont = NULL;
 CMS_ContentInfo *cms;

 cms = SMIME_read_CMS(in, &cont);


The MIME parser used by SMIME_read_CMS() is somewhat primitive.  While it will handle most S/MIME messages more complex compound formats may not work.

The parser assumes that the CMS_ContentInfo structure is always base64 encoded and will not handle the case where it is in binary format or uses quoted printable format.

The use of a memory BIO to hold the signed content limits the size of message which can be processed due to memory restraints: a streaming single pass option should be available.

Return Values

SMIME_read_CMS_ex() and SMIME_read_CMS() return a valid CMS_ContentInfo structure or NULL if an error occurred. The error can be obtained from ERR_get_error(3).

See Also

ERR_get_error(3), CMS_sign(3), CMS_verify(3), CMS_encrypt(3), CMS_decrypt(3)


The function SMIME_read_CMS_ex() was added in OpenSSL 3.0.

Referenced By

The man page SMIME_read_CMS_ex.3ossl(3) is an alias of SMIME_read_CMS.3ossl(3).

2023-10-26 3.1.4 OpenSSL