- NAME
- SYNOPSIS
- DESCRIPTION
- RETURN VALUES
- CIPHER LISTING
- AEAD INTERFACE

- GCM and OCB Modes
- CCM Mode
- SIV Mode
- ChaCha20-Poly1305

- NOTES
- BUGS
- EXAMPLES
- SEE ALSO
- HISTORY
- COPYRIGHT

# 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

# SYNOPSIS

     #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);

# DESCRIPTION

The EVP cipher routines are a high level interface to certain symmetric ciphers.

The EVP_CIPHER type is a structure for cipher method implementation.

`EVP_CIPHER_fetch()` fetches the cipher implementation for the given algorithm from any provider offering it, within the criteria given by the properties. See 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 EVP_CIPHER structure.

`EVP_CIPHER_free()` decrements the reference count for the 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 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 ctx for encryption with cipher type. type is typically supplied by a function such as EVP_aes_256_cbc(), or a value explicitly fetched with `EVP_CIPHER_fetch()`. If impl is non-NULL, its implementation of the cipher type is used if there is one, and if not, the default implementation is used. key is the symmetric key to use and 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 type in an initial call and supply the remaining parameters in subsequent calls, all of which have 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 inl bytes from the buffer in and writes the encrypted version to 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 out should contain sufficient room. The actual number of bytes written is placed in outl. It also checks if in and 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 out which should have sufficient space for one cipher block. The number of bytes written is placed in 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 out passed to `EVP_DecryptUpdate()` should have sufficient room for (inl + cipher_block_size) bytes unless the cipher block size is 1 in which case 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 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 ctx itself. This function should be called anytime 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 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 inl amount of bytes from in and leaves the result in out. If the cipher doesn't have the flag EVP_CIPH_FLAG_CUSTOM_CIPHER set, then 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 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 EVP_CIPHER or 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 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 params from a cipher.

`EVP_CIPHER_CTX_set_params()` Sets the list of operation params into a CIPHER context ctx.

`EVP_CIPHER_CTX_get_params()` retrieves the requested list of operation params from CIPHER context ctx.

`EVP_CIPHER_gettable_params()`, `EVP_CIPHER_gettable_ctx_params()`, and `EVP_CIPHER_settable_ctx_params()` get a constant 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 OSSL_PARAM(3) for the use of 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 EVP_CIPHER or EVP_CIPHER_CTX structure. The constant 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 EVP_CIPHER or EVP_CIPHER_CTX. It will return zero if the cipher does not use an IV. The constant 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 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 EVP_CIPHER or EVP_CIPHER_CTX structure. The constant 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 NID_undef.

`EVP_CIPHER_is_a()` returns 1 if cipher is an implementation of an algorithm that's identifiable with name, otherwise 0. If 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 OPENSSL_CTX(3)) will be considered.

`EVP_CIPHER_number()` returns the internal dynamic number assigned to the cipher. This is only useful with fetched EVP_CIPHERs.

`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 cipher, and calls fn with each name and data. This is only useful with fetched EVP_CIPHERs.

`EVP_CIPHER_provider()` returns an OSSL_PROVIDER pointer to the provider that implements the given EVP_CIPHER.

`EVP_CIPHER_CTX_cipher()` returns the EVP_CIPHER structure when passed an 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. 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 libctx, and for each of the implementations, calls the given function fn with the implementation method and the given arg as argument.

# RETURN VALUES

`EVP_CIPHER_fetch()` returns a pointer to a EVP_CIPHER for success and 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 EVP_CIPHER_CTX for success and 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 EVP_CIPH_FLAG_CUSTOM_CIPHER is set for the cipher. `EVP_Cipher()` returns 1 on success or 0 on failure, if the flag 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 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 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.

# CIPHER LISTING

All algorithms have a fixed key length unless otherwise stated.

Refer to SEE ALSO for the full list of ciphers available through the EVP interface.

`EVP_enc_null()`

  Null cipher: does nothing.

# AEAD INTERFACE

The EVP interface for Authenticated Encryption with Associated Data (AEAD) modes are subtly altered and several additional 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 out set to 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 MUST NOT be used as it is corrupted.

## GCM and OCB Modes

The following ctrls are supported in GCM and OCB modes.

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.

EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_AEAD_GET_TAG, taglen, tag)

  Writes `taglen` bytes of the tag value to the buffer indicated by `tag`. This call can only be made when encrypting data and after all data has been processed (e.g. after an `EVP_EncryptFinal()` call).

  For OCB, `taglen` must either be 16 or the value previously set via EVP_CTRL_AEAD_SET_TAG.

EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_AEAD_SET_TAG, taglen, tag)

  Sets the expected tag to `taglen` bytes from `tag`. The tag length can only be set before specifying an IV. `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 `tag` set to `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.

## CCM Mode

The EVP interface for CCM mode is similar to that of the GCM mode but with a few additional requirements and different ctrl values.

For CCM mode, the total plaintext or ciphertext length MUST be passed to `EVP_CipherUpdate()`, `EVP_EncryptUpdate()` or `EVP_DecryptUpdate()` with the output and input parameters (in and out) set to NULL and the length passed in the inl parameter.

The following ctrls are supported in CCM mode.

EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_AEAD_SET_TAG, taglen, tag)

  This call is made to set the expected CCM tag value when decrypting or the length of the tag (with the `tag` parameter set to NULL) when encrypting. The tag length is often referred to as 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 AEAD INTERFACE).

EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_CCM_SET_L, ivlen, NULL)

  Sets the CCM L value. If not set a default is used (8 for AES).

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 15 - L so it is 7 by default for AES.

## 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 out set to 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 MUST NOT be used as it is corrupted.

The following ctrls are supported in both SIV modes.

EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_AEAD_GET_TAG, taglen, tag);

  Writes taglen bytes of the tag value to the buffer indicated by tag. This call can only be made when encrypting data and after all data has been processed (e.g. after an `EVP_EncryptFinal()` call). For SIV mode the taglen must be 16.

EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_AEAD_SET_TAG, taglen, tag);

  Sets the expected tag to taglen bytes from tag. This call is only legal when decrypting data and must be made before any data is processed (e.g. before any `EVP_DecryptUpdate()` call). For SIV mode the taglen must be 16.

SIV mode makes two passes over the input data, thus, only one call to `EVP_CipherUpdate()`, `EVP_EncryptUpdate()` or `EVP_DecryptUpdate()` should be made with out set to a non-NULL value. A call to `EVP_Decrypt_Final()` or `EVP_CipherFinal()` is not required, but will indicate if the update operation succeeded.

## ChaCha20-Poly1305

The following ctrls are supported for the ChaCha20-Poly1305 AEAD algorithm.

EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_AEAD_SET_IVLEN, ivlen, NULL)

  Sets the nonce length. This call can only be made before specifying the nonce. If not called a default nonce length of 12 (i.e. 96 bits) is used. The maximum nonce length is 12 bytes (i.e. 96-bits). If a nonce of less than 12 bytes is set then the nonce is automatically padded with leading 0 bytes to make it 12 bytes in length.

EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_AEAD_GET_TAG, taglen, tag)

  Writes `taglen` bytes of the tag value to the buffer indicated by `tag`. This call can only be made when encrypting data and after all data has been processed (e.g. after an `EVP_EncryptFinal()` call).

  `taglen` specified here must be 16 (POLY1305_BLOCK_SIZE, i.e. 128-bits) or less.

EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_AEAD_SET_TAG, taglen, tag)

  Sets the expected tag to `taglen` bytes from `tag`. The tag length can only be set before specifying an IV. `taglen` must be between 1 and 16 (POLY1305_BLOCK_SIZE) inclusive. This call is only valid when decrypting data.

# NOTES

Where possible the EVP interface to symmetric ciphers should be used in preference to the low level interfaces. This is because the code then becomes transparent to the cipher used and much more flexible. Additionally, the EVP interface will ensure the use of platform specific cryptographic acceleration such as AES-NI (the low level interfaces do not provide the guarantee).

PKCS padding works by adding n padding bytes of value n to make the total length of the encrypted data a multiple of the block size. Padding is always added so if the data is already a multiple of the block size n will equal the block size. For example if the block size is 8 and 11 bytes are to be encrypted then 5 padding bytes of value 5 will be added.

When decrypting the final block is checked to see if it has the correct form.

Although the decryption operation can produce an error if padding is enabled, it is not a strong test that the input data or key is correct. A random block has better than 1 in 256 chance of being of the correct format and problems with the input data earlier on will not produce a final decrypt error.

If padding is disabled then the decryption operation will always succeed if the total amount of data decrypted is a multiple of the block size.

The functions `EVP_EncryptInit()`, `EVP_EncryptFinal()`, `EVP_DecryptInit()`, `EVP_CipherInit()` and `EVP_CipherFinal()` are obsolete but are retained for compatibility with existing code. New code should use `EVP_EncryptInit_ex()`, `EVP_EncryptFinal_ex()`, `EVP_DecryptInit_ex()`, `EVP_DecryptFinal_ex()`, `EVP_CipherInit_ex()` and `EVP_CipherFinal_ex()` because they can reuse an existing context without allocating and freeing it up on each call.

There are some differences between functions `EVP_CipherInit()` and `EVP_CipherInit_ex()`, significant in some circumstances. `EVP_CipherInit()` fills the passed context object with zeros. As a consequence, `EVP_CipherInit()` does not allow step-by-step initialization of the ctx when the key and iv are passed in separate calls. It also means that the flags set for the CTX are removed, and it is especially important for the EVP_CIPHER_CTX_FLAG_WRAP_ALLOW flag treated specially in `EVP_CipherInit_ex()`.

`EVP_get_cipherbynid()`, and `EVP_get_cipherbyobj()` are implemented as macros.

# BUGS

EVP_MAX_KEY_LENGTH and EVP_MAX_IV_LENGTH only refer to the internal ciphers with default key lengths. If custom ciphers exceed these values the results are unpredictable. This is because it has become standard practice to define a generic key as a fixed unsigned char array containing EVP_MAX_KEY_LENGTH bytes.

The ASN1 code is incomplete (and sometimes inaccurate) it has only been tested for certain common S/MIME ciphers (RC2, DES, triple DES) in CBC mode.

# EXAMPLES

Encrypt a string using IDEA:

     int do_crypt(char *outfile)
     {
         unsigned char outbuf[1024];
         int outlen, tmplen;
         /*
          * Bogus key and IV: we'd normally set these from
          * another source.
          */
         unsigned char key[] = {0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15};
         unsigned char iv[] = {1,2,3,4,5,6,7,8};
         char intext[] = "Some Crypto Text";
         EVP_CIPHER_CTX *ctx;
         FILE *out;

         ctx = EVP_CIPHER_CTX_new();
         EVP_EncryptInit_ex(ctx, EVP_idea_cbc(), NULL, key, iv);

         if (!EVP_EncryptUpdate(ctx, outbuf, &outlen, intext, strlen(intext))) {
             /* Error */
             EVP_CIPHER_CTX_free(ctx);
             return 0;
         }
         /*
          * Buffer passed to EVP_EncryptFinal() must be after data just
          * encrypted to avoid overwriting it.
          */
         if (!EVP_EncryptFinal_ex(ctx, outbuf + outlen, &tmplen)) {
             /* Error */
             EVP_CIPHER_CTX_free(ctx);
             return 0;
         }
         outlen += tmplen;
         EVP_CIPHER_CTX_free(ctx);
         /*
          * Need binary mode for fopen because encrypted data is
          * binary data. Also cannot use strlen() on it because
          * it won't be NUL terminated and may contain embedded
          * NULs.
          */
         out = fopen(outfile, "wb");
         if (out == NULL) {
             /* Error */
             return 0;
         }
         fwrite(outbuf, 1, outlen, out);
         fclose(out);
         return 1;
     }

The ciphertext from the above example can be decrypted using the openssl utility with the command line (shown on two lines for clarity):

     openssl idea -d \
         -K 000102030405060708090A0B0C0D0E0F -iv 0102030405060708 <filename

General encryption and decryption function example using FILE I/O and AES128 with a 128-bit key:

     int do_crypt(FILE *in, FILE *out, int do_encrypt)
     {
         /* Allow enough space in output buffer for additional block */
         unsigned char inbuf[1024], outbuf[1024 + EVP_MAX_BLOCK_LENGTH];
         int inlen, outlen;
         EVP_CIPHER_CTX *ctx;
         /*
          * Bogus key and IV: we'd normally set these from
          * another source.
          */
         unsigned char key[] = "0123456789abcdeF";
         unsigned char iv[] = "1234567887654321";

         /* Don't set key or IV right away; we want to check lengths */
         ctx = EVP_CIPHER_CTX_new();
         EVP_CipherInit_ex(&ctx, EVP_aes_128_cbc(), NULL, NULL, NULL,
                           do_encrypt);
         OPENSSL_assert(EVP_CIPHER_CTX_key_length(ctx) == 16);
         OPENSSL_assert(EVP_CIPHER_CTX_iv_length(ctx) == 16);

         /* Now we can set key and IV */
         EVP_CipherInit_ex(ctx, NULL, NULL, key, iv, do_encrypt);

         for (;;) {
             inlen = fread(inbuf, 1, 1024, in);
             if (inlen <= 0)
                 break;
             if (!EVP_CipherUpdate(ctx, outbuf, &outlen, inbuf, inlen)) {
                 /* Error */
                 EVP_CIPHER_CTX_free(ctx);
                 return 0;
             }
             fwrite(outbuf, 1, outlen, out);
         }
         if (!EVP_CipherFinal_ex(ctx, outbuf, &outlen)) {
             /* Error */
             EVP_CIPHER_CTX_free(ctx);
             return 0;
         }
         fwrite(outbuf, 1, outlen, out);

         EVP_CIPHER_CTX_free(ctx);
         return 1;
     }

# SEE ALSO

evp(7)

Supported ciphers are listed in:

EVP_aes_128_gcm(3), EVP_aria_128_gcm(3), EVP_bf_cbc(3), EVP_camellia_128_ecb(3), EVP_cast5_cbc(3), EVP_chacha20(3), EVP_des_cbc(3), EVP_desx_cbc(3), EVP_idea_cbc(3), EVP_rc2_cbc(3), EVP_rc4(3), EVP_rc5_32_12_16_cbc(3), EVP_seed_cbc(3), EVP_sm4_cbc(3)

# HISTORY

Support for OCB mode was added in OpenSSL 1.1.0.

EVP_CIPHER_CTX was made opaque in OpenSSL 1.1.0. As a result, `EVP_CIPHER_CTX_reset()` appeared and `EVP_CIPHER_CTX_cleanup()` disappeared. `EVP_CIPHER_CTX_init()` remains as an alias for `EVP_CIPHER_CTX_reset()`.

The `EVP_CIPHER_fetch()`, `EVP_CIPHER_free()`, `EVP_CIPHER_up_ref()`, `EVP_CIPHER_CTX_set_params()` and `EVP_CIPHER_CTX_get_params()` functions were added in 3.0.

# COPYRIGHT

Copyright 2000-2018 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 https://www.openssl.org/source/license.html.