BIO_NEW_CMS(3) | Library Functions Manual | BIO_NEW_CMS(3)

# NAME

`BIO_new_CMS` — CMS streaming filter BIO

# SYNOPSIS

library “libcrypto”
`#include <openssl/cms.h>`

BIO *
`BIO_new_CMS`(BIO *out, CMS_ContentInfo *cms);

# DESCRIPTION

`BIO_new_CMS`() returns a streaming filter BIO chain based on cms. The output of the filter is written to out. Any data written to the chain is automatically translated to a BER format CMS structure of the appropriate type.

The chain returned by this function behaves like a standard filter BIO. It supports non blocking I/O. Content is processed and streamed on the fly and not all held in memory at once: so it is possible to encode very large structures. After all content has been written through the chain, BIO_flush(3) must be called to finalise the structure.

The `CMS_STREAM` flag must be included in the corresponding flags parameter of the cms creation function.

If an application wishes to write additional data to out, BIOs should be removed from the chain using BIO_pop(3) and freed with BIO_free(3) until out is reached. If no additional data needs to be written, BIO_free_all(3) can be called to free up the whole chain.

Any content written through the filter is used verbatim: no canonical translation is performed.

It is possible to chain multiple BIOs to, for example, create a triple wrapped signed, enveloped, signed structure. In this case it is the application's responsibility to set the inner content type of any outer CMS_ContentInfo structures.

Large numbers of small writes through the chain should be avoided as this will produce an output consisting of lots of OCTET STRING structures. Prepending a BIO_f_buffer(3) buffering BIO will prevent this.

# RETURN VALUES

`BIO_new_CMS`() returns a BIO chain when successful or `NULL` if an error occurred. The error can be obtained from ERR_get_error(3).

# SEE ALSO

BIO_new(3), CMS_ContentInfo_new(3), CMS_encrypt(3), CMS_sign(3)

# HISTORY

`BIO_new_CMS`() first appeared in OpenSSL 1.0.0 and has been available since OpenBSD 6.7.

# BUGS

There is currently no corresponding inverse BIO which can decode a CMS structure on the fly.

June 8, 2025 | Debian