doc/man3/CMS_decrypt.pod - third_party/openssl - Git at Google

 =pod

 =head1 NAME

 CMS_decrypt, CMS_decrypt_set1_pkey_and_peer,
 CMS_decrypt_set1_pkey, CMS_decrypt_set1_password
 - decrypt content from a CMS envelopedData structure

 =head1 SYNOPSIS

  #include <openssl/cms.h>

  int CMS_decrypt(CMS_ContentInfo *cms, EVP_PKEY *pkey, X509 *cert,
                  BIO *dcont, BIO *out, unsigned int flags);
  int CMS_decrypt_set1_pkey_and_peer(CMS_ContentInfo *cms,
                  EVP_PKEY *pk, X509 *cert, X509 *peer);
  int CMS_decrypt_set1_pkey(CMS_ContentInfo *cms, EVP_PKEY *pk, X509 *cert);
  int CMS_decrypt_set1_password(CMS_ContentInfo *cms,
                                unsigned char *pass, ossl_ssize_t passlen);

 =head1 DESCRIPTION

 CMS_decrypt() extracts the decrypted content from a CMS EnvelopedData
 or AuthEnvelopedData structure.
 It uses CMS_decrypt_set1_pkey() to decrypt the content
 with the recipient private key I<pkey> if I<pkey> is not NULL.
 In this case, the associated certificate is recommended to provide in I<cert> -
 see the NOTES below.
 I<out> is a BIO to write the content to and
 I<flags> is an optional set of flags.
 If I<pkey> is NULL the function assumes that decryption was already done
 (e.g., using CMS_decrypt_set1_pkey() or CMS_decrypt_set1_password()) and just
 provides the content unless I<cert>, I<dcont>, and I<out> are NULL as well.
 The I<dcont> parameter is used in the rare case where the encrypted content
 is detached. It will normally be set to NULL.

 CMS_decrypt_set1_pkey_and_peer() decrypts the CMS_ContentInfo structure I<cms>
 using the private key I<pkey>, the corresponding certificate I<cert>, which is
 recommended but may be NULL, and the (optional) originator certificate I<peer>.
 On success, it also records in I<cms> the decryption key I<pkey>, and then
 should be followed by C<CMS_decrypt(cms, NULL, NULL, dcont, out, flags)>.
 This call deallocates any decryption key stored in I<cms>.

 CMS_decrypt_set1_pkey() is the same as
 CMS_decrypt_set1_pkey_and_peer() with I<peer> being NULL.

 CMS_decrypt_set1_password() decrypts the CMS_ContentInfo structure I<cms>
 using the secret I<pass> of length I<passlen>.
 On success, it also records in I<cms> the decryption key used, and then
 should be followed by C<CMS_decrypt(cms, NULL, NULL, dcont, out, flags)>.
 This call deallocates any decryption key stored in I<cms>.

 =head1 NOTES

 Although the recipients certificate is not needed to decrypt the data it is
 needed to locate the appropriate (of possible several) recipients in the CMS
 structure.

 If I<cert> is set to NULL all possible recipients are tried. This case however
 is problematic. To thwart the MMA attack (Bleichenbacher's attack on
 PKCS #1 v1.5 RSA padding) all recipients are tried whether they succeed or
 not. If no recipient succeeds then a random symmetric key is used to decrypt
 the content: this will typically output garbage and may (but is not guaranteed
 to) ultimately return a padding error only. If CMS_decrypt() just returned an
 error when all recipient encrypted keys failed to decrypt an attacker could
 use this in a timing attack. If the special flag B<CMS_DEBUG_DECRYPT> is set
 then the above behaviour is modified and an error B<is> returned if no
 recipient encrypted key can be decrypted B<without> generating a random
 content encryption key. Applications should use this flag with
 B<extreme caution> especially in automated gateways as it can leave them
 open to attack.

 It is possible to determine the correct recipient key by other means (for
 example looking them up in a database) and setting them in the CMS structure
 in advance using the CMS utility functions such as CMS_set1_pkey(),
 or use CMS_decrypt_set1_password() if the recipient has a symmetric key.
 In these cases both I<cert> and I<pkey> should be set to NULL.

 To process KEKRecipientInfo types CMS_set1_key() or CMS_RecipientInfo_set0_key()
 and CMS_RecipientInfo_decrypt() should be called before CMS_decrypt() and
 I<cert> and I<pkey> set to NULL.

 The following flags can be passed in the I<flags> parameter.

 If the B<CMS_TEXT> flag is set MIME headers for type C<text/plain> are deleted
 from the content. If the content is not of type C<text/plain> then an error is
 returned.

 =head1 RETURN VALUES

 CMS_decrypt(), CMS_decrypt_set1_pkey_and_peer(),
 CMS_decrypt_set1_pkey(), and CMS_decrypt_set1_password()
 return either 1 for success or 0 for failure.
 The error can be obtained from ERR_get_error(3).

 =head1 BUGS

 The B<set1_> part of these function names is misleading
 and should better read: B<with_>.

 The lack of single pass processing and the need to hold all data in memory as
 mentioned in CMS_verify() also applies to CMS_decrypt().

 =head1 SEE ALSO

 L<ERR_get_error(3)>, L<CMS_encrypt(3)>

 =head1 HISTORY

 CMS_decrypt_set1_pkey_and_peer() and CMS_decrypt_set1_password()
 were added in OpenSSL 3.0.

 =head1 COPYRIGHT

 Copyright 2008-2020 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
 L<https://www.openssl.org/source/license.html>.

 =cut
	=pod

	=head1 NAME

	CMS_decrypt, CMS_decrypt_set1_pkey_and_peer,
	CMS_decrypt_set1_pkey, CMS_decrypt_set1_password
	- decrypt content from a CMS envelopedData structure

	=head1 SYNOPSIS

	#include <openssl/cms.h>

	int CMS_decrypt(CMS_ContentInfo cms, EVP_PKEY pkey, X509 *cert,
	BIO dcont, BIO out, unsigned int flags);
	int CMS_decrypt_set1_pkey_and_peer(CMS_ContentInfo *cms,
	EVP_PKEY pk, X509 cert, X509 *peer);
	int CMS_decrypt_set1_pkey(CMS_ContentInfo cms, EVP_PKEY pk, X509 *cert);
	int CMS_decrypt_set1_password(CMS_ContentInfo *cms,
	unsigned char *pass, ossl_ssize_t passlen);

	=head1 DESCRIPTION

	CMS_decrypt() extracts the decrypted content from a CMS EnvelopedData
	or AuthEnvelopedData structure.
	It uses CMS_decrypt_set1_pkey() to decrypt the content
	with the recipient private key I<pkey> if I<pkey> is not NULL.
	In this case, the associated certificate is recommended to provide in I<cert> -
	see the NOTES below.
	I<out> is a BIO to write the content to and
	I<flags> is an optional set of flags.
	If I<pkey> is NULL the function assumes that decryption was already done
	(e.g., using CMS_decrypt_set1_pkey() or CMS_decrypt_set1_password()) and just
	provides the content unless I<cert>, I<dcont>, and I<out> are NULL as well.
	The I<dcont> parameter is used in the rare case where the encrypted content
	is detached. It will normally be set to NULL.

	CMS_decrypt_set1_pkey_and_peer() decrypts the CMS_ContentInfo structure I<cms>
	using the private key I<pkey>, the corresponding certificate I<cert>, which is
	recommended but may be NULL, and the (optional) originator certificate I<peer>.
	On success, it also records in I<cms> the decryption key I<pkey>, and then
	should be followed by C<CMS_decrypt(cms, NULL, NULL, dcont, out, flags)>.
	This call deallocates any decryption key stored in I<cms>.

	CMS_decrypt_set1_pkey() is the same as
	CMS_decrypt_set1_pkey_and_peer() with I<peer> being NULL.

	CMS_decrypt_set1_password() decrypts the CMS_ContentInfo structure I<cms>
	using the secret I<pass> of length I<passlen>.
	On success, it also records in I<cms> the decryption key used, and then
	should be followed by C<CMS_decrypt(cms, NULL, NULL, dcont, out, flags)>.
	This call deallocates any decryption key stored in I<cms>.

	=head1 NOTES

	Although the recipients certificate is not needed to decrypt the data it is
	needed to locate the appropriate (of possible several) recipients in the CMS
	structure.

	If I<cert> is set to NULL all possible recipients are tried. This case however
	is problematic. To thwart the MMA attack (Bleichenbacher's attack on
	PKCS #1 v1.5 RSA padding) all recipients are tried whether they succeed or
	not. If no recipient succeeds then a random symmetric key is used to decrypt
	the content: this will typically output garbage and may (but is not guaranteed
	to) ultimately return a padding error only. If CMS_decrypt() just returned an
	error when all recipient encrypted keys failed to decrypt an attacker could
	use this in a timing attack. If the special flag B<CMS_DEBUG_DECRYPT> is set
	then the above behaviour is modified and an error B<is> returned if no
	recipient encrypted key can be decrypted B<without> generating a random
	content encryption key. Applications should use this flag with
	B<extreme caution> especially in automated gateways as it can leave them
	open to attack.

	It is possible to determine the correct recipient key by other means (for
	example looking them up in a database) and setting them in the CMS structure
	in advance using the CMS utility functions such as CMS_set1_pkey(),
	or use CMS_decrypt_set1_password() if the recipient has a symmetric key.
	In these cases both I<cert> and I<pkey> should be set to NULL.

	To process KEKRecipientInfo types CMS_set1_key() or CMS_RecipientInfo_set0_key()
	and CMS_RecipientInfo_decrypt() should be called before CMS_decrypt() and
	I<cert> and I<pkey> set to NULL.

	The following flags can be passed in the I<flags> parameter.

	If the B<CMS_TEXT> flag is set MIME headers for type C<text/plain> are deleted
	from the content. If the content is not of type C<text/plain> then an error is
	returned.

	=head1 RETURN VALUES

	CMS_decrypt(), CMS_decrypt_set1_pkey_and_peer(),
	CMS_decrypt_set1_pkey(), and CMS_decrypt_set1_password()
	return either 1 for success or 0 for failure.
	The error can be obtained from ERR_get_error(3).

	=head1 BUGS

	The B<set1_> part of these function names is misleading
	and should better read: B<with_>.

	The lack of single pass processing and the need to hold all data in memory as
	mentioned in CMS_verify() also applies to CMS_decrypt().

	=head1 SEE ALSO

	L<ERR_get_error(3)>, L<CMS_encrypt(3)>

	=head1 HISTORY

	CMS_decrypt_set1_pkey_and_peer() and CMS_decrypt_set1_password()
	were added in OpenSSL 3.0.

	=head1 COPYRIGHT

	Copyright 2008-2020 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
	L<https://www.openssl.org/source/license.html>.

	=cut