---
name: "SMIME_read_ASN1"
section: "3ssl"
platform: "linux"
package: "openssl"
version: "3.6.5-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/SMIME_read_ASN1"
---

# SMIME\_read\_ASN1(3ssl)

parse S/MIME message

## NAME

SMIME\_read\_ASN1\_ex, SMIME\_read\_ASN1 - parse S/MIME message

## SYNOPSIS

```
 #include <openssl/asn1.h>
 ASN1_VALUE *SMIME_read_ASN1_ex(BIO *in, int flags, BIO **bcont,
                                const ASN1_ITEM *it, ASN1_VALUE **x,
                                OSSL_LIB_CTX *libctx, const char *propq);
 ASN1_VALUE *SMIME_read_ASN1(BIO *in, BIO **bcont, const ASN1_ITEM *it);
```

## DESCRIPTION

**SMIME\_read\_ASN1\_ex()** parses a message in S/MIME format.

*in* is a BIO to read the message from. 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. *x* can be used to optionally supply a previously created *it* ASN1\_VALUE object (such as CMS\_ContentInfo or PKCS7), it can be set to NULL. Valid values that can be used by ASN.1 structure *it* are ASN1\_ITEM\_rptr(PKCS7) or ASN1\_ITEM\_rptr(CMS\_ContentInfo). Any algorithm fetches that occur during the operation will use the **OSSL\_LIB\_CTX** supplied in the *libctx* parameter, and use the property query string *propq* See "ALGORITHM FETCHING" in [**crypto**(7)](/crypto/7.md) for further details about algorithm fetching.

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 ASN1\_VALUE structure is returned or NULL if an error occurred.

**SMIME\_read\_ASN1()** is similar to **SMIME\_read\_ASN1\_ex()** but sets the value of *x* to NULL and the value of *flags* to 0.

## NOTES

The higher level functions **SMIME\_read\_CMS\_ex**(3) and **SMIME\_read\_PKCS7\_ex**(3) should be used instead of **SMIME\_read\_ASN1\_ex()**.

To support future functionality if *bcont* is not NULL *\*bcont* should be initialized to NULL.

## BUGS

The MIME parser used by **SMIME\_read\_ASN1\_ex()** is somewhat primitive. While it will handle most S/MIME messages more complex compound formats may not work.

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\_ASN1\_ex()** and **SMIME\_read\_ASN1()** return a valid **ASN1\_VALUE** structure or **NULL** if an error occurred. The error can be obtained from **ERR\_get\_error**(3).

## SEE ALSO

**ERR\_get\_error**(3), **SMIME\_read\_CMS\_ex**(3), **SMIME\_read\_PKCS7\_ex**(3), **SMIME\_write\_ASN1**(3), **SMIME\_write\_ASN1\_ex**(3)

## HISTORY

The function **SMIME\_read\_ASN1\_ex()** was added in OpenSSL 3.0.

## COPYRIGHT

Copyright 2020-2021 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 \<https://www.openssl.org/source/license.html\>.