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|
=pod
=head1 NAME
EVP_CIPHER_fetch,
EVP_CIPHER_up_ref,
EVP_CIPHER_free,
EVP_CIPHER_CTX_new,
EVP_CIPHER_CTX_reset,
EVP_CIPHER_CTX_free,
EVP_EncryptInit_ex,
EVP_EncryptUpdate,
EVP_EncryptFinal_ex,
EVP_DecryptInit_ex,
EVP_DecryptUpdate,
EVP_DecryptFinal_ex,
EVP_CipherInit_ex,
EVP_CipherUpdate,
EVP_CipherFinal_ex,
EVP_CIPHER_CTX_set_key_length,
EVP_CIPHER_CTX_ctrl,
EVP_EncryptInit,
EVP_EncryptFinal,
EVP_DecryptInit,
EVP_DecryptFinal,
EVP_CipherInit,
EVP_CipherFinal,
EVP_Cipher,
EVP_get_cipherbyname,
EVP_get_cipherbynid,
EVP_get_cipherbyobj,
EVP_CIPHER_is_a,
EVP_CIPHER_name,
EVP_CIPHER_number,
EVP_CIPHER_names_do_all,
EVP_CIPHER_provider,
EVP_CIPHER_nid,
EVP_CIPHER_get_params,
EVP_CIPHER_gettable_params,
EVP_CIPHER_block_size,
EVP_CIPHER_key_length,
EVP_CIPHER_iv_length,
EVP_CIPHER_flags,
EVP_CIPHER_mode,
EVP_CIPHER_type,
EVP_CIPHER_CTX_cipher,
EVP_CIPHER_CTX_name,
EVP_CIPHER_CTX_nid,
EVP_CIPHER_CTX_get_params,
EVP_CIPHER_gettable_ctx_params,
EVP_CIPHER_CTX_set_params,
EVP_CIPHER_settable_ctx_params,
EVP_CIPHER_CTX_block_size,
EVP_CIPHER_CTX_key_length,
EVP_CIPHER_CTX_iv_length,
EVP_CIPHER_CTX_tag_length,
EVP_CIPHER_CTX_get_app_data,
EVP_CIPHER_CTX_set_app_data,
EVP_CIPHER_CTX_type,
EVP_CIPHER_CTX_flags,
EVP_CIPHER_CTX_mode,
EVP_CIPHER_param_to_asn1,
EVP_CIPHER_asn1_to_param,
EVP_CIPHER_CTX_set_padding,
EVP_enc_null,
EVP_CIPHER_do_all_provided
- EVP cipher routines
=head1 SYNOPSIS
=for openssl generic
#include <openssl/evp.h>
EVP_CIPHER *EVP_CIPHER_fetch(OPENSSL_CTX *ctx, const char *algorithm,
const char *properties);
int EVP_CIPHER_up_ref(EVP_CIPHER *cipher);
void EVP_CIPHER_free(EVP_CIPHER *cipher);
EVP_CIPHER_CTX *EVP_CIPHER_CTX_new(void);
int EVP_CIPHER_CTX_reset(EVP_CIPHER_CTX *ctx);
void EVP_CIPHER_CTX_free(EVP_CIPHER_CTX *ctx);
int EVP_EncryptInit_ex(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type,
ENGINE *impl, const unsigned char *key, const unsigned char *iv);
int EVP_EncryptUpdate(EVP_CIPHER_CTX *ctx, unsigned char *out,
int *outl, const unsigned char *in, int inl);
int EVP_EncryptFinal_ex(EVP_CIPHER_CTX *ctx, unsigned char *out, int *outl);
int EVP_DecryptInit_ex(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type,
ENGINE *impl, const unsigned char *key, const unsigned char *iv);
int EVP_DecryptUpdate(EVP_CIPHER_CTX *ctx, unsigned char *out,
int *outl, const unsigned char *in, int inl);
int EVP_DecryptFinal_ex(EVP_CIPHER_CTX *ctx, unsigned char *outm, int *outl);
int EVP_CipherInit_ex(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type,
ENGINE *impl, const unsigned char *key, const unsigned char *iv, int enc);
int EVP_CipherUpdate(EVP_CIPHER_CTX *ctx, unsigned char *out,
int *outl, const unsigned char *in, int inl);
int EVP_CipherFinal_ex(EVP_CIPHER_CTX *ctx, unsigned char *outm, int *outl);
int EVP_EncryptInit(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type,
const unsigned char *key, const unsigned char *iv);
int EVP_EncryptFinal(EVP_CIPHER_CTX *ctx, unsigned char *out, int *outl);
int EVP_DecryptInit(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type,
const unsigned char *key, const unsigned char *iv);
int EVP_DecryptFinal(EVP_CIPHER_CTX *ctx, unsigned char *outm, int *outl);
int EVP_CipherInit(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type,
const unsigned char *key, const unsigned char *iv, int enc);
int EVP_CipherFinal(EVP_CIPHER_CTX *ctx, unsigned char *outm, int *outl);
int EVP_Cipher(EVP_CIPHER_CTX *ctx, unsigned char *out,
const unsigned char *in, unsigned int inl);
int EVP_CIPHER_CTX_set_padding(EVP_CIPHER_CTX *x, int padding);
int EVP_CIPHER_CTX_set_key_length(EVP_CIPHER_CTX *x, int keylen);
int EVP_CIPHER_CTX_ctrl(EVP_CIPHER_CTX *ctx, int type, int arg, void *ptr);
int EVP_CIPHER_CTX_rand_key(EVP_CIPHER_CTX *ctx, unsigned char *key);
const EVP_CIPHER *EVP_get_cipherbyname(const char *name);
const EVP_CIPHER *EVP_get_cipherbynid(int nid);
const EVP_CIPHER *EVP_get_cipherbyobj(const ASN1_OBJECT *a);
int EVP_CIPHER_nid(const EVP_CIPHER *e);
int EVP_CIPHER_number(const EVP_CIPHER *e);
int EVP_CIPHER_is_a(const EVP_CIPHER *cipher, const char *name);
void EVP_CIPHER_names_do_all(const EVP_CIPHER *cipher,
void (*fn)(const char *name, void *data),
void *data);
const char *EVP_CIPHER_name(const EVP_CIPHER *cipher);
const OSSL_PROVIDER *EVP_CIPHER_provider(const EVP_CIPHER *cipher);
int EVP_CIPHER_block_size(const EVP_CIPHER *e);
int EVP_CIPHER_key_length(const EVP_CIPHER *e);
int EVP_CIPHER_iv_length(const EVP_CIPHER *e);
unsigned long EVP_CIPHER_flags(const EVP_CIPHER *e);
unsigned long EVP_CIPHER_mode(const EVP_CIPHER *e);
int EVP_CIPHER_type(const EVP_CIPHER *ctx);
const EVP_CIPHER *EVP_CIPHER_CTX_cipher(const EVP_CIPHER_CTX *ctx);
int EVP_CIPHER_CTX_nid(const EVP_CIPHER_CTX *ctx);
const char *EVP_CIPHER_CTX_name(const EVP_CIPHER_CTX *ctx);
int EVP_CIPHER_get_params(EVP_CIPHER *cipher, OSSL_PARAM params[]);
int EVP_CIPHER_CTX_set_params(EVP_CIPHER_CTX *ctx, const OSSL_PARAM params[]);
int EVP_CIPHER_CTX_get_params(EVP_CIPHER_CTX *ctx, OSSL_PARAM params[]);
const OSSL_PARAM *EVP_CIPHER_gettable_params(const EVP_CIPHER *cipher);
const OSSL_PARAM *EVP_CIPHER_settable_ctx_params(const EVP_CIPHER *cipher);
const OSSL_PARAM *EVP_CIPHER_gettable_ctx_params(const EVP_CIPHER *cipher);
int EVP_CIPHER_CTX_block_size(const EVP_CIPHER_CTX *ctx);
int EVP_CIPHER_CTX_key_length(const EVP_CIPHER_CTX *ctx);
int EVP_CIPHER_CTX_iv_length(const EVP_CIPHER_CTX *ctx);
int EVP_CIPHER_CTX_tag_length(const EVP_CIPHER_CTX *ctx);
void *EVP_CIPHER_CTX_get_app_data(const EVP_CIPHER_CTX *ctx);
void EVP_CIPHER_CTX_set_app_data(const EVP_CIPHER_CTX *ctx, void *data);
int EVP_CIPHER_CTX_type(const EVP_CIPHER_CTX *ctx);
int EVP_CIPHER_CTX_mode(const EVP_CIPHER_CTX *ctx);
int EVP_CIPHER_param_to_asn1(EVP_CIPHER_CTX *c, ASN1_TYPE *type);
int EVP_CIPHER_asn1_to_param(EVP_CIPHER_CTX *c, ASN1_TYPE *type);
void EVP_CIPHER_do_all_provided(OPENSSL_CTX *libctx,
void (*fn)(EVP_CIPHER *cipher, void *arg),
void *arg);
=head1 DESCRIPTION
The EVP cipher routines are a high level interface to certain
symmetric ciphers.
The B<EVP_CIPHER> type is a structure for cipher method implementation.
EVP_CIPHER_fetch() fetches the cipher implementation for the given
B<algorithm> from any provider offering it, within the criteria given
by the B<properties>.
See L<provider(7)/Fetching algorithms> for further information.
The returned value must eventually be freed with EVP_CIPHER_free().
EVP_CIPHER_up_ref() increments the reference count for an B<EVP_CIPHER>
structure.
EVP_CIPHER_free() decrements the reference count for the B<EVP_CIPHER>
structure.
If the reference count drops to 0 then the structure is freed.
EVP_CIPHER_CTX_new() creates a cipher context.
EVP_CIPHER_CTX_free() clears all information from a cipher context
and free up any allocated memory associate with it, including B<ctx>
itself. This function should be called after all operations using a
cipher are complete so sensitive information does not remain in
memory.
EVP_EncryptInit_ex() sets up cipher context B<ctx> for encryption
with cipher B<type>. B<type> is typically supplied by a function such
as EVP_aes_256_cbc(), or a value explicitly fetched with
EVP_CIPHER_fetch(). If B<impl> is non-NULL, its implementation of the
cipher B<type> is used if there is one, and if not, the default
implementation is used. B<key> is the symmetric key to use
and B<iv> is the IV to use (if necessary), the actual number of bytes
used for the key and IV depends on the cipher. It is possible to set
all parameters to NULL except B<type> in an initial call and supply
the remaining parameters in subsequent calls, all of which have B<type>
set to NULL. This is done when the default cipher parameters are not
appropriate.
For EVP_CIPH_GCM_MODE the IV will be generated internally if it is not
specified.
EVP_EncryptUpdate() encrypts B<inl> bytes from the buffer B<in> and
writes the encrypted version to B<out>. This function can be called
multiple times to encrypt successive blocks of data. The amount
of data written depends on the block alignment of the encrypted data:
as a result the amount of data written may be anything from zero bytes
to (inl + cipher_block_size - 1) so B<out> should contain sufficient
room. The actual number of bytes written is placed in B<outl>. It also
checks if B<in> and B<out> are partially overlapping, and if they are
0 is returned to indicate failure.
If padding is enabled (the default) then EVP_EncryptFinal_ex() encrypts
the "final" data, that is any data that remains in a partial block.
It uses standard block padding (aka PKCS padding) as described in
the NOTES section, below. The encrypted
final data is written to B<out> which should have sufficient space for
one cipher block. The number of bytes written is placed in B<outl>. After
this function is called the encryption operation is finished and no further
calls to EVP_EncryptUpdate() should be made.
If padding is disabled then EVP_EncryptFinal_ex() will not encrypt any more
data and it will return an error if any data remains in a partial block:
that is if the total data length is not a multiple of the block size.
EVP_DecryptInit_ex(), EVP_DecryptUpdate() and EVP_DecryptFinal_ex() are the
corresponding decryption operations. EVP_DecryptFinal() will return an
error code if padding is enabled and the final block is not correctly
formatted. The parameters and restrictions are identical to the encryption
operations except that if padding is enabled the decrypted data buffer B<out>
passed to EVP_DecryptUpdate() should have sufficient room for
(B<inl> + cipher_block_size) bytes unless the cipher block size is 1 in
which case B<inl> bytes is sufficient.
EVP_CipherInit_ex(), EVP_CipherUpdate() and EVP_CipherFinal_ex() are
functions that can be used for decryption or encryption. The operation
performed depends on the value of the B<enc> parameter. It should be set
to 1 for encryption, 0 for decryption and -1 to leave the value unchanged
(the actual value of 'enc' being supplied in a previous call).
EVP_CIPHER_CTX_reset() clears all information from a cipher context
and free up any allocated memory associate with it, except the B<ctx>
itself. This function should be called anytime B<ctx> is to be reused
for another EVP_CipherInit() / EVP_CipherUpdate() / EVP_CipherFinal()
series of calls.
EVP_EncryptInit(), EVP_DecryptInit() and EVP_CipherInit() behave in a
similar way to EVP_EncryptInit_ex(), EVP_DecryptInit_ex() and
EVP_CipherInit_ex() except they always use the default cipher implementation.
EVP_EncryptFinal(), EVP_DecryptFinal() and EVP_CipherFinal() are
identical to EVP_EncryptFinal_ex(), EVP_DecryptFinal_ex() and
EVP_CipherFinal_ex(). In previous releases they also cleaned up
the B<ctx>, but this is no longer done and EVP_CIPHER_CTX_clean()
must be called to free any context resources.
EVP_Cipher() encrypts or decrypts a maximum I<inl> amount of bytes from
I<in> and leaves the result in I<out>.
If the cipher doesn't have the flag B<EVP_CIPH_FLAG_CUSTOM_CIPHER> set,
then I<inl> must be a multiple of EVP_CIPHER_block_size(). If it isn't,
the result is undefined. If the cipher has that flag set, then I<inl>
can be any size.
This function is historic and shouldn't be used in an application, please
consider using EVP_CipherUpdate() and EVP_CipherFinal_ex instead.
EVP_get_cipherbyname(), EVP_get_cipherbynid() and EVP_get_cipherbyobj()
return an EVP_CIPHER structure when passed a cipher name, a NID or an
ASN1_OBJECT structure.
EVP_CIPHER_nid() and EVP_CIPHER_CTX_nid() return the NID of a cipher when
passed an B<EVP_CIPHER> or B<EVP_CIPHER_CTX> structure. The actual NID
value is an internal value which may not have a corresponding OBJECT
IDENTIFIER.
EVP_CIPHER_CTX_set_padding() enables or disables padding. This
function should be called after the context is set up for encryption
or decryption with EVP_EncryptInit_ex(), EVP_DecryptInit_ex() or
EVP_CipherInit_ex(). By default encryption operations are padded using
standard block padding and the padding is checked and removed when
decrypting. If the B<pad> parameter is zero then no padding is
performed, the total amount of data encrypted or decrypted must then
be a multiple of the block size or an error will occur.
EVP_CIPHER_get_params() retrieves the requested list of algorithm
B<params> from a B<cipher>.
EVP_CIPHER_CTX_set_params() Sets the list of operation B<params> into a CIPHER
context B<ctx>.
EVP_CIPHER_CTX_get_params() retrieves the requested list of operation
B<params> from CIPHER context B<ctx>.
EVP_CIPHER_gettable_params(), EVP_CIPHER_gettable_ctx_params(), and
EVP_CIPHER_settable_ctx_params() get a constant B<OSSL_PARAM> array
that describes the retrievable and settable parameters, i.e. parameters
that can be used with EVP_CIPHER_get_params(), EVP_CIPHER_CTX_get_params()
and EVP_CIPHER_CTX_set_params(), respectively.
See L<OSSL_PARAM(3)> for the use of B<OSSL_PARAM> as parameter descriptor.
EVP_CIPHER_key_length() and EVP_CIPHER_CTX_key_length() return the key
length of a cipher when passed an B<EVP_CIPHER> or B<EVP_CIPHER_CTX>
structure. The constant B<EVP_MAX_KEY_LENGTH> is the maximum key length
for all ciphers. Note: although EVP_CIPHER_key_length() is fixed for a
given cipher, the value of EVP_CIPHER_CTX_key_length() may be different
for variable key length ciphers.
EVP_CIPHER_CTX_set_key_length() sets the key length of the cipher ctx.
If the cipher is a fixed length cipher then attempting to set the key
length to any value other than the fixed value is an error.
EVP_CIPHER_iv_length() and EVP_CIPHER_CTX_iv_length() return the IV
length of a cipher when passed an B<EVP_CIPHER> or B<EVP_CIPHER_CTX>.
It will return zero if the cipher does not use an IV. The constant
B<EVP_MAX_IV_LENGTH> is the maximum IV length for all ciphers.
EVP_CIPHER_CTX_tag_length() returns the tag length of a AEAD cipher when passed
a B<EVP_CIPHER_CTX>. It will return zero if the cipher does not support a tag.
It returns a default value if the tag length has not been set.
EVP_CIPHER_block_size() and EVP_CIPHER_CTX_block_size() return the block
size of a cipher when passed an B<EVP_CIPHER> or B<EVP_CIPHER_CTX>
structure. The constant B<EVP_MAX_BLOCK_LENGTH> is also the maximum block
length for all ciphers.
EVP_CIPHER_type() and EVP_CIPHER_CTX_type() return the type of the passed
cipher or context. This "type" is the actual NID of the cipher OBJECT
IDENTIFIER as such it ignores the cipher parameters and 40 bit RC2 and
128 bit RC2 have the same NID. If the cipher does not have an object
identifier or does not have ASN1 support this function will return
B<NID_undef>.
EVP_CIPHER_is_a() returns 1 if I<cipher> is an implementation of an
algorithm that's identifiable with I<name>, otherwise 0.
If I<cipher> is a legacy cipher (it's the return value from the likes
of EVP_aes128() rather than the result of an EVP_CIPHER_fetch()), only
cipher names registered with the default library context (see
L<OPENSSL_CTX(3)>) will be considered.
EVP_CIPHER_number() returns the internal dynamic number assigned to
the I<cipher>. This is only useful with fetched B<EVP_CIPHER>s.
EVP_CIPHER_name() and EVP_CIPHER_CTX_name() return the name of the passed
cipher or context. For fetched ciphers with multiple names, only one
of them is returned; it's recommended to use EVP_CIPHER_names_do_all()
instead.
EVP_CIPHER_names_do_all() traverses all names for the I<cipher>, and
calls I<fn> with each name and I<data>. This is only useful with
fetched B<EVP_CIPHER>s.
EVP_CIPHER_provider() returns an B<OSSL_PROVIDER> pointer to the provider
that implements the given B<EVP_CIPHER>.
EVP_CIPHER_CTX_cipher() returns the B<EVP_CIPHER> structure when passed
an B<EVP_CIPHER_CTX> structure.
EVP_CIPHER_mode() and EVP_CIPHER_CTX_mode() return the block cipher mode:
EVP_CIPH_ECB_MODE, EVP_CIPH_CBC_MODE, EVP_CIPH_CFB_MODE, EVP_CIPH_OFB_MODE,
EVP_CIPH_CTR_MODE, EVP_CIPH_GCM_MODE, EVP_CIPH_CCM_MODE, EVP_CIPH_XTS_MODE,
EVP_CIPH_WRAP_MODE, EVP_CIPH_OCB_MODE or EVP_CIPH_SIV_MODE. If the cipher is a
stream cipher then EVP_CIPH_STREAM_CIPHER is returned.
EVP_CIPHER_flags() returns any flags associated with the cipher. See
EVP_CIPHER_meth_set_flags() for a list of currently defined flags.
EVP_CIPHER_param_to_asn1() sets the AlgorithmIdentifier "parameter" based
on the passed cipher. This will typically include any parameters and an
IV. The cipher IV (if any) must be set when this call is made. This call
should be made before the cipher is actually "used" (before any
EVP_EncryptUpdate(), EVP_DecryptUpdate() calls for example). This function
may fail if the cipher does not have any ASN1 support.
EVP_CIPHER_asn1_to_param() sets the cipher parameters based on an ASN1
AlgorithmIdentifier "parameter". The precise effect depends on the cipher
In the case of RC2, for example, it will set the IV and effective key length.
This function should be called after the base cipher type is set but before
the key is set. For example EVP_CipherInit() will be called with the IV and
key set to NULL, EVP_CIPHER_asn1_to_param() will be called and finally
EVP_CipherInit() again with all parameters except the key set to NULL. It is
possible for this function to fail if the cipher does not have any ASN1 support
or the parameters cannot be set (for example the RC2 effective key length
is not supported.
EVP_CIPHER_CTX_ctrl() allows various cipher specific parameters to be determined
and set.
EVP_CIPHER_CTX_rand_key() generates a random key of the appropriate length
based on the cipher context. The EVP_CIPHER can provide its own random key
generation routine to support keys of a specific form. B<Key> must point to a
buffer at least as big as the value returned by EVP_CIPHER_CTX_key_length().
EVP_CIPHER_do_all_provided() traverses all ciphers implemented by all activated
providers in the given library context I<libctx>, and for each of the
implementations, calls the given function I<fn> with the implementation method
and the given I<arg> as argument.
=head1 RETURN VALUES
EVP_CIPHER_fetch() returns a pointer to a B<EVP_CIPHER> for success
and B<NULL> for failure.
EVP_CIPHER_up_ref() returns 1 for success or 0 otherwise.
EVP_CIPHER_CTX_new() returns a pointer to a newly created
B<EVP_CIPHER_CTX> for success and B<NULL> for failure.
EVP_EncryptInit_ex(), EVP_EncryptUpdate() and EVP_EncryptFinal_ex()
return 1 for success and 0 for failure.
EVP_DecryptInit_ex() and EVP_DecryptUpdate() return 1 for success and 0 for failure.
EVP_DecryptFinal_ex() returns 0 if the decrypt failed or 1 for success.
EVP_CipherInit_ex() and EVP_CipherUpdate() return 1 for success and 0 for failure.
EVP_CipherFinal_ex() returns 0 for a decryption failure or 1 for success.
EVP_Cipher() returns the amount of encrypted / decrypted bytes, or -1
on failure, if the flag B<EVP_CIPH_FLAG_CUSTOM_CIPHER> is set for the
cipher. EVP_Cipher() returns 1 on success or 0 on failure, if the flag
B<EVP_CIPH_FLAG_CUSTOM_CIPHER> is not set for the cipher.
EVP_CIPHER_CTX_reset() returns 1 for success and 0 for failure.
EVP_get_cipherbyname(), EVP_get_cipherbynid() and EVP_get_cipherbyobj()
return an B<EVP_CIPHER> structure or NULL on error.
EVP_CIPHER_nid() and EVP_CIPHER_CTX_nid() return a NID.
EVP_CIPHER_block_size() and EVP_CIPHER_CTX_block_size() return the block
size.
EVP_CIPHER_key_length() and EVP_CIPHER_CTX_key_length() return the key
length.
EVP_CIPHER_CTX_set_padding() always returns 1.
EVP_CIPHER_iv_length() and EVP_CIPHER_CTX_iv_length() return the IV
length or zero if the cipher does not use an IV.
EVP_CIPHER_CTX_tag_length() return the tag length or zero if the cipher does not
use a tag.
EVP_CIPHER_type() and EVP_CIPHER_CTX_type() return the NID of the cipher's
OBJECT IDENTIFIER or NID_undef if it has no defined OBJECT IDENTIFIER.
EVP_CIPHER_CTX_cipher() returns an B<EVP_CIPHER> structure.
EVP_CIPHER_param_to_asn1() and EVP_CIPHER_asn1_to_param() return greater
than zero for success and zero or a negative number on failure.
EVP_CIPHER_CTX_rand_key() returns 1 for success.
=head1 CIPHER LISTING
All algorithms have a fixed key length unless otherwise stated.
Refer to L</SEE ALSO> for the full list of ciphers available through the EVP
interface.
=over 4
=item EVP_enc_null()
Null cipher: does nothing.
=back
=head1 AEAD INTERFACE
The EVP interface for Authenticated Encryption with Associated Data (AEAD)
modes are subtly altered and several additional I<ctrl> operations are supported
depending on the mode specified.
To specify additional authenticated data (AAD), a call to EVP_CipherUpdate(),
EVP_EncryptUpdate() or EVP_DecryptUpdate() should be made with the output
parameter B<out> set to B<NULL>.
When decrypting, the return value of EVP_DecryptFinal() or EVP_CipherFinal()
indicates whether the operation was successful. If it does not indicate success,
the authentication operation has failed and any output data B<MUST NOT> be used
as it is corrupted.
=head2 GCM and OCB Modes
The following I<ctrl>s are supported in GCM and OCB modes.
=over 4
=item EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_AEAD_SET_IVLEN, ivlen, NULL)
Sets the IV length. This call can only be made before specifying an IV. If
not called a default IV length is used.
For GCM AES and OCB AES the default is 12 (i.e. 96 bits). For OCB mode the
maximum is 15.
=item EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_AEAD_GET_TAG, taglen, tag)
Writes C<taglen> bytes of the tag value to the buffer indicated by C<tag>.
This call can only be made when encrypting data and B<after> all data has been
processed (e.g. after an EVP_EncryptFinal() call).
For OCB, C<taglen> must either be 16 or the value previously set via
B<EVP_CTRL_AEAD_SET_TAG>.
=item EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_AEAD_SET_TAG, taglen, tag)
Sets the expected tag to C<taglen> bytes from C<tag>.
The tag length can only be set before specifying an IV.
C<taglen> must be between 1 and 16 inclusive.
For GCM, this call is only valid when decrypting data.
For OCB, this call is valid when decrypting data to set the expected tag,
and before encryption to set the desired tag length.
In OCB mode, calling this before encryption with C<tag> set to C<NULL> sets the
tag length. If this is not called prior to encryption, a default tag length is
used.
For OCB AES, the default tag length is 16 (i.e. 128 bits). It is also the
maximum tag length for OCB.
=back
=head2 CCM Mode
The EVP interface for CCM mode is similar to that of the GCM mode but with a
few additional requirements and different I<ctrl> values.
For CCM mode, the total plaintext or ciphertext length B<MUST> be passed to
EVP_CipherUpdate(), EVP_EncryptUpdate() or EVP_DecryptUpdate() with the output
and input parameters (B<in> and B<out>) set to B<NULL> and the length passed in
the B<inl> parameter.
The following I<ctrl>s are supported in CCM mode.
=over 4
=item EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_AEAD_SET_TAG, taglen, tag)
This call is made to set the expected B<CCM> tag value when decrypting or
the length of the tag (with the C<tag> parameter set to NULL) when encrypting.
The tag length is often referred to as B<M>. If not set a default value is
used (12 for AES). When decrypting, the tag needs to be set before passing
in data to be decrypted, but as in GCM and OCB mode, it can be set after
passing additional authenticated data (see L</AEAD INTERFACE>).
=item EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_CCM_SET_L, ivlen, NULL)
Sets the CCM B<L> value. If not set a default is used (8 for AES).
=item EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_AEAD_SET_IVLEN, ivlen, NULL)
Sets the CCM nonce (IV) length. This call can only be made before specifying an
nonce value. The nonce length is given by B<15 - L> so it is 7 by default for
AES.
=back
=head2 SIV Mode
For SIV mode ciphers the behaviour of the EVP interface is subtly
altered and several additional ctrl operations are supported.
To specify any additional authenticated data (AAD) and/or a Nonce, a call to
EVP_CipherUpdate(), EVP_EncryptUpdate() or EVP_DecryptUpdate() should be made
with the output parameter B<out> set to B<NULL>.
RFC5297 states that the Nonce is the last piece of AAD before the actual
encrypt/decrypt takes place. The API does not differentiate the Nonce from
other AAD.
When decrypting the return value of EVP_DecryptFinal() or EVP_CipherFinal()
indicates if the operation was successful. If it does not indicate success
the authentication operation has failed and any output data B<MUST NOT>
be used as it is corrupted.
The following ctrls are supported in both SIV modes.
=over 4
=item EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_AEAD_GET_TAG, taglen, tag);
Writes B<taglen> bytes of the tag value to the buffer indicated by B<tag>.
This call can only be made when encrypting data and B<after> all data has been
processed (e.g. after an EVP_EncryptFinal() call). For SIV mode the taglen must
be 16.
=item EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_AEAD_SET_TAG, taglen, tag);
Sets the expected tag to B<taglen> bytes from B<tag>. This call is only legal
whe
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