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115 lines
4.5 KiB
Plaintext
115 lines
4.5 KiB
Plaintext
=pod
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=head1 NAME
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CMS_encrypt_ex, CMS_encrypt - create a CMS envelopedData structure
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=head1 SYNOPSIS
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#include <openssl/cms.h>
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CMS_ContentInfo *CMS_encrypt_ex(STACK_OF(X509) *certs, BIO *in,
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const EVP_CIPHER *cipher, unsigned int flags,
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OSSL_LIB_CTX *libctx, const char *propq);
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CMS_ContentInfo *CMS_encrypt(STACK_OF(X509) *certs, BIO *in,
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const EVP_CIPHER *cipher, unsigned int flags);
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=head1 DESCRIPTION
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CMS_encrypt_ex() creates and returns a CMS EnvelopedData or
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AuthEnvelopedData structure. I<certs> is a list of recipient certificates.
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I<in> is the content to be encrypted. I<cipher> is the symmetric cipher to use.
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I<flags> is an optional set of flags. The library context I<libctx> and the
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property query I<propq> are used internally when retrieving algorithms from
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providers.
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Only certificates carrying RSA, Diffie-Hellman or EC keys are supported by this
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function.
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EVP_des_ede3_cbc() (triple DES) is the algorithm of choice for S/MIME use
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because most clients will support it.
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The algorithm passed in the B<cipher> parameter must support ASN1 encoding of
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its parameters. If the cipher mode is GCM, then an AuthEnvelopedData structure
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containing MAC is used. Otherwise an EnvelopedData structure is used. Currently
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the AES variants with GCM mode are the only supported AEAD algorithms.
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Many browsers implement a "sign and encrypt" option which is simply an S/MIME
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envelopedData containing an S/MIME signed message. This can be readily produced
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by storing the S/MIME signed message in a memory BIO and passing it to
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CMS_encrypt().
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The following flags can be passed in the B<flags> parameter.
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If the B<CMS_TEXT> flag is set MIME headers for type B<text/plain> are
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prepended to the data.
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Normally the supplied content is translated into MIME canonical format (as
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required by the S/MIME specifications) if B<CMS_BINARY> is set no translation
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occurs. This option should be used if the supplied data is in binary format
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otherwise the translation will corrupt it. If B<CMS_BINARY> is set then
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B<CMS_TEXT> is ignored.
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OpenSSL will by default identify recipient certificates using issuer name
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and serial number. If B<CMS_USE_KEYID> is set it will use the subject key
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identifier value instead. An error occurs if all recipient certificates do not
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have a subject key identifier extension.
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If the B<CMS_STREAM> flag is set a partial B<CMS_ContentInfo> structure is
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returned suitable for streaming I/O: no data is read from the BIO B<in>.
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If the B<CMS_PARTIAL> flag is set a partial B<CMS_ContentInfo> structure is
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returned to which additional recipients and attributes can be added before
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finalization.
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The data being encrypted is included in the CMS_ContentInfo structure, unless
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B<CMS_DETACHED> is set in which case it is omitted. This is rarely used in
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practice and is not supported by SMIME_write_CMS().
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If the flag B<CMS_STREAM> is set the returned B<CMS_ContentInfo> structure is
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B<not> complete and outputting its contents via a function that does not
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properly finalize the B<CMS_ContentInfo> structure will give unpredictable
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results.
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Several functions including SMIME_write_CMS(), i2d_CMS_bio_stream(),
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PEM_write_bio_CMS_stream() finalize the structure. Alternatively finalization
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can be performed by obtaining the streaming ASN1 B<BIO> directly using
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BIO_new_CMS().
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The recipients specified in B<certs> use a CMS KeyTransRecipientInfo info
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structure. KEKRecipientInfo is also supported using the flag B<CMS_PARTIAL>
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and CMS_add0_recipient_key().
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The parameter B<certs> may be NULL if B<CMS_PARTIAL> is set and recipients
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added later using CMS_add1_recipient_cert() or CMS_add0_recipient_key().
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CMS_encrypt() is similar to CMS_encrypt_ex() but uses default values
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of NULL for the library context I<libctx> and the property query I<propq>.
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=head1 RETURN VALUES
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CMS_encrypt_ex() and CMS_encrypt() return either a CMS_ContentInfo
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structure or NULL if an error occurred. The error can be obtained from
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ERR_get_error(3).
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=head1 SEE ALSO
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L<ERR_get_error(3)>, L<CMS_decrypt(3)>
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=head1 HISTORY
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The function CMS_encrypt_ex() was added in OpenSSL 3.0.
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The B<CMS_STREAM> flag was first supported in OpenSSL 1.0.0.
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=head1 COPYRIGHT
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Copyright 2008-2020 The OpenSSL Project Authors. All Rights Reserved.
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Licensed under the Apache License 2.0 (the "License"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file LICENSE in the source distribution or at
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L<https://www.openssl.org/source/license.html>.
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=cut
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