openssl/doc/man7/provider-cipher.pod

=pod

=head1 NAME

provider-cipher - The cipher library E<lt>-E<gt> provider functions

=head1 SYNOPSIS

=for comment multiple includes

 #include <openssl/core_numbers.h>
 #include <openssl/core_names.h>

 /*
  * None of these are actual functions, but are displayed like this for
  * the function signatures for functions that are offered as function
  * pointers in OSSL_DISPATCH arrays.
  */

 /* Context management */
 void *OP_cipher_newctx(void *provctx);
 void OP_cipher_freectx(void *cctx);
 void *OP_cipher_dupctx(void *cctx);

 /* Encryption/decryption */
 int OP_cipher_encrypt_init(void *cctx, const unsigned char *key,
                            size_t keylen, const unsigned char *iv,
                            size_t ivlen);
 int OP_cipher_decrypt_init(void *cctx, const unsigned char *key,
                            size_t keylen, const unsigned char *iv,
                            size_t ivlen);
 int OP_cipher_update(void *cctx, unsigned char *out, size_t *outl,
                      size_t outsize, const unsigned char *in, size_t inl);
 int OP_cipher_final(void *cctx, unsigned char *out, size_t *outl,
                     size_t outsize);
 int OP_cipher_cipher(void *cctx, unsigned char *out, size_t *outl,
                      size_t outsize, const unsigned char *in, size_t inl);

 /* Cipher parameter descriptors */
 const OSSL_PARAM *OP_cipher_gettable_params(void);

 /* Cipher operation parameter descriptors */
 const OSSL_PARAM *OP_cipher_gettable_ctx_params(void);
 const OSSL_PARAM *OP_cipher_settable_ctx_params(void);

 /* Cipher parameters */
 int OP_cipher_get_params(OSSL_PARAM params[]);

 /* Cipher operation parameters */
 int OP_cipher_get_ctx_params(void *cctx, OSSL_PARAM params[]);
 int OP_cipher_set_ctx_params(void *cctx, const OSSL_PARAM params[]);

=head1 DESCRIPTION

This documentation is primarily aimed at provider authors. See L<provider(7)>
for further information.

The CIPHER operation enables providers to implement cipher algorithms and make
them available to applications via the API functions L<EVP_EncryptInit_ex(3)>,
L<EVP_EncryptUpdate(3)> and L<EVP_EncryptFinal(3)> (as well as the decrypt
equivalents and other related functions).

All "functions" mentioned here are passed as function pointers between
F<libcrypto> and the provider in B<OSSL_DISPATCH> arrays via
B<OSSL_ALGORITHM> arrays that are returned by the provider's
provider_query_operation() function
(see L<provider-base(7)/Provider Functions>).

All these "functions" have a corresponding function type definition
named B<OSSL_{name}_fn>, and a helper function to retrieve the
function pointer from an B<OSSL_DISPATCH> element named
B<OSSL_get_{name}>.
For example, the "function" OP_cipher_newctx() has these:

 typedef void *(OSSL_OP_cipher_newctx_fn)(void *provctx);
 static ossl_inline OSSL_OP_cipher_newctx_fn
     OSSL_get_OP_cipher_newctx(const OSSL_DISPATCH *opf);

B<OSSL_DISPATCH> arrays are indexed by numbers that are provided as
macros in L<openssl-core_numbers.h(7)>, as follows:

 OP_cipher_newctx               OSSL_FUNC_CIPHER_NEWCTX
 OP_cipher_freectx              OSSL_FUNC_CIPHER_FREECTX
 OP_cipher_dupctx               OSSL_FUNC_CIPHER_DUPCTX

 OP_cipher_encrypt_init         OSSL_FUNC_CIPHER_ENCRYPT_INIT
 OP_cipher_decrypt_init         OSSL_FUNC_CIPHER_DECRYPT_INIT
 OP_cipher_update               OSSL_FUNC_CIPHER_UPDATE
 OP_cipher_final                OSSL_FUNC_CIPHER_FINAL
 OP_cipher_cipher               OSSL_FUNC_CIPHER_CIPHER

 OP_cipher_get_params           OSSL_FUNC_CIPHER_GET_PARAMS
 OP_cipher_get_ctx_params       OSSL_FUNC_CIPHER_GET_CTX_PARAMS
 OP_cipher_set_ctx_params       OSSL_FUNC_CIPHER_SET_CTX_PARAMS

 OP_cipher_gettable_params      OSSL_FUNC_CIPHER_GETTABLE_PARAMS
 OP_cipher_gettable_ctx_params  OSSL_FUNC_CIPHER_GETTABLE_CTX_PARAMS
 OP_cipher_settable_ctx_params  OSSL_FUNC_CIPHER_SETTABLE_CTX_PARAMS

A cipher algorithm implementation may not implement all of these functions.
In order to be a consistent set of functions there must at least be a complete
set of "encrypt" functions, or a complete set of "decrypt" functions, or a
single "cipher" function.
In all cases both the OP_cipher_newctx and OP_cipher_freectx functions must be
present.
All other functions are optional.

=head2 Context Management Functions

OP_cipher_newctx() should create and return a pointer to a provider side
structure for holding context information during a cipher operation.
A pointer to this context will be passed back in a number of the other cipher
operation function calls.
The parameter B<provctx> is the provider context generated during provider
initialisation (see L<provider(3)>).

OP_cipher_freectx() is passed a pointer to the provider side cipher context in
the B<cctx> parameter.
This function should free any resources associated with that context.

OP_cipher_dupctx() should duplicate the provider side cipher context in the
B<cctx> parameter and return the duplicate copy.

=head2 Encryption/Decryption Functions

OP_cipher_encrypt_init() initialises a cipher operation for encryption given a
newly created provider side cipher context in the B<cctx> parameter.
The key to be used is given in B<key> which is B<keylen> bytes long.
The IV to be used is given in B<iv> which is B<ivlen> bytes long.

OP_cipher_decrypt_init() is the same as OP_cipher_encrypt_init() except that it
initialises the context for a decryption operation.

OP_cipher_update() is called to supply data to be encrypted/decrypted as part of
a previously initialised cipher operation.
The B<cctx> parameter contains a pointer to a previously initialised provider
side context.
OP_cipher_update() should encrypt/decrypt B<inl> bytes of data at the location
pointed to by B<in>.
The encrypted data should be stored in B<out> and the amount of data written to
B<*outl> which should not exceed B<outsize> bytes.
OP_cipher_update() may be called multiple times for a single cipher operation.
It is the responsibility of the cipher implementation to handle input lengths
that are not multiples of the block length.
In such cases a cipher implementation will typically cache partial blocks of
input data until a complete block is obtained.
B<out> may be the same location as B<in> but it should not partially overlap.
The same expectations apply to B<outsize> as documented for
L<EVP_EncryptUpdate(3)> and L<EVP_DecryptUpdate(3)>.

OP_cipher_final() completes an encryption or decryption started through previous
OP_cipher_encrypt_init() or OP_cipher_decrypt_init(), and OP_cipher_update()
calls.
The B<cctx> parameter contains a pointer to the provider side context.
Any final encryption/decryption output should be written to B<out> and the
amount of data written to B<*outl> which should not exceed B<outsize> bytes.
The same expectations apply to B<outsize> as documented for
L<EVP_EncryptFinal(3)> and L<EVP_DecryptFinal(3)>.

OP_cipher_cipher() performs encryption/decryption using the provider side cipher
context in the B<cctx> parameter that should have been previously initialised via
a call to OP_cipher_encrypt_init() or OP_cipher_decrypt_init.
This should call the raw underlying cipher function without any padding.
This will be invoked in the provider as a result of the application calling
L<EVP_Cipher(3)>.
The application is responsible for ensuring that the input is a multiple of the
block length.
The data to be encrypted/decrypted will be in B<in>, and it will be B<inl> bytes
in length.
The output from the encryption/decryption should be stored in B<out> and the
amount of data stored should be put in B<*outl> which should be no more than
B<outsize> bytes.

=head2 Cipher Parameters

See L<OSSL_PARAM(3)> for further details on the parameters structure used by
these functions.

OP_cipher_get_params() gets details of the algorithm implementation
and stores them in B<params>.

OP_cipher_set_ctx_params() sets cipher operation parameters for the
provider side cipher context B<cctx> to B<params>.
Any parameter settings are additional to any that were previously set.

OP_cipher_get_ctx_params() gets cipher operation details details from
the given provider side cipher context B<cctx> and stores them in B<params>.

OP_cipher_gettable_params(), OP_cipher_gettable_ctx_params(), and
OP_cipher_settable_ctx_params() all return constant B<OSSL_PARAM> arrays
as descriptors of the parameters that OP_cipher_get_params(),
OP_cipher_get_ctx_params(), and OP_cipher_set_ctx_params() can handle,
respectively.

Parameters currently recognised by built-in ciphers are as follows. Not all
parameters are relevant to, or are understood by all ciphers:

=over 4

=item B<OSSL_CIPHER_PARAM_PADDING> (uint)

Sets the padding mode for the associated cipher ctx.
Setting a value of 1 will turn padding on.
Setting a value of 0 will turn padding off.

=item B<OSSL_CIPHER_PARAM_MODE> (uint)

Gets the mode for the associated cipher algorithm.
See L<EVP_CIPHER_mode(3)> for a list of valid modes.

=item B<OSSL_CIPHER_PARAM_BLOCK_SIZE> (size_t)

Gets the block size for the associated cipher algorithm.
The block size should be 1 for stream ciphers.
Note that the block size for a cipher may be different to the block size for
the underlying encryption/decryption primitive.
For example AES in CTR mode has a block size of 1 (because it operates like a
stream cipher), even though AES has a block size of 16.

=item B<OSSL_CIPHER_PARAM_FLAGS> (ulong)

Gets any flags for the associated cipher algorithm.
See L<EVP_CIPHER_meth_set_flags(3)> for a list of currently defined cipher
flags.

=item B<OSSL_CIPHER_PARAM_KEYLEN> (size_t)

Gets the key length for the associated cipher algorithm.
This can also be used to get or set the key length for the associated cipher
ctx.

=item B<OSSL_CIPHER_PARAM_IVLEN> (size_t)

Gets the IV length for the associated cipher algorithm.

=item B<OSSL_CIPHER_PARAM_IV> (octet_string OR octet_ptr)

Gets the IV for the associated cipher ctx.

=item B<OSSL_CIPHER_PARAM_NUM> (uint)

Gets or sets the cipher specific "num" parameter for the associated cipher ctx.
Built-in ciphers typically use this to track how much of the current underlying
block has been "used" already.

=item B<OSSL_CIPHER_PARAM_AEAD_TAG> (octet_string)

Gets or sets the AEAD tag for the associated cipher ctx.
See L<EVP_EncryptInit(3)/AEAD Interface>.

=item B<OSSL_CIPHER_PARAM_AEAD_TAGLEN> (size_t)

Gets the tag length to be used for an AEAD cipher for the associated cipher ctx.
It returns a default value if it has not been set.

=item B<OSSL_CIPHER_PARAM_AEAD_TLS1_AAD> (octet_string)

=for comment TODO(3.0): Consider changing this interface so that all ciphers
use the standard AEAD interface - rather than having this special purpose
interface for TLS

Sets TLSv1.2 AAD information for the associated cipher ctx.
TLSv1.2 AAD information is always 13 bytes in length and is as defined for the
"additional_data" field described in section 6.2.3.3 of RFC5246.

=item B<OSSL_CIPHER_PARAM_AEAD_TLS1_AAD_PAD> (size_t)

Gets the length of the tag that will be added to a TLS record for the AEAD
tag for the associated cipher ctx.

=item B<OSSL_CIPHER_PARAM_AEAD_TLS1_IV_FIXED> (octet_string)

=for comment TODO(3.0): This interface needs completely redesigning!

Sets the fixed portion of an IV for an AEAD cipher used in a TLS record
encryption/ decryption for the associated cipher ctx.
TLS record encryption/decryption always occurs "in place" so that the input and
output buffers are always the same memory location.
AEAD IVs in TLSv1.2 consist of an implicit "fixed" part and an explicit part
that varies with every record.
Setting a TLS fixed IV changes a cipher to encrypt/decrypt TLS records.
TLS records are encrypted/decrypted using a single OP_cipher_cipher call per
record.
For a record decryption the first bytes of the input buffer will be the explict
part of the IV and the final bytes of the input buffer will be the AEAD tag.
The length of the explicit part of the IV and the tag length will depend on the
cipher in use and will be defined in the RFC for the relevant ciphersuite.
In order to allow for "in place" decryption the plaintext output should be
written to the same location in the output buffer that the ciphertext payload
was read from, i.e. immediately after the explicit IV.

When encrypting a record the first bytes of the input buffer will be empty to
allow space for the explicit IV, as will the final bytes where the tag will
be written.
The length of the input buffer will include the length of the explicit IV, the
payload, and the tag bytes.
The cipher implementation should generate the explicit IV and write it to the
beginning of the output buffer, do "in place" encryption of the payload and
write that to the output buffer, and finally add the tag onto the end of the
output buffer.

Whether encrypting or decrypting the value written to B<*outl> in the
OP_cipher_cipher call should be the length of the payload excluding the explicit
IV length and the tag length.

=item B<OSSL_CIPHER_PARAM_AEAD_IVLEN> (size_t)

Sets the IV length to be used for an AEAD cipher for the associated cipher ctx.

=item B<OSSL_CIPHER_PARAM_RANDOM_KEY> (octet_string)

Gets a implementation specific randomly generated key for the associated
cipher ctx. This is currently only supported by 3DES (which sets the key to
odd parity).

=back

=head1 RETURN VALUES

OP_cipher_newctx() and OP_cipher_dupctx() should return the newly created
provider side cipher context, or NULL on failure.

OP_cipher_encrypt_init(), OP_cipher_decrypt_init(), OP_cipher_update(),
OP_cipher_final(), OP_cipher_cipher(), OP_cipher_get_params(),
OP_cipher_get_ctx_params() and OP_cipher_set_ctx_params() should return 1 for
success or 0 on error.

OP_cipher_gettable_params(), OP_cipher_gettable_ctx_params() and
OP_cipher_settable_ctx_params() should return a constant B<OSSL_PARAM>
array, or NULL if none is offered.

=head1 SEE ALSO

L<provider(7)>

=head1 HISTORY

The provider CIPHER interface was introduced in OpenSSL 3.0.

=head1 COPYRIGHT

Copyright 2019 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