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## 5.4 General cipher functions

To work with the algorithms, several functions are available to map algorithm names to the internal identifiers, as well as ways to retrieve information about an algorithm or the current cipher context.

- Function:
*gcry_error_t***gcry_cipher_algo_info***(int*`algo`, int`what`, void *`buffer`, size_t *`nbytes`) -
This function is used to retrieve information on a specific algorithm. You pass the cipher algorithm ID as

`algo`and the type of information requested as`what`. The result is either returned as the return code of the function or copied to the provided`buffer`whose allocated length must be available in an integer variable with the address passed in`nbytes`. This variable will also receive the actual used length of the buffer.Here is a list of supported codes for

`what`:`GCRYCTL_GET_KEYLEN:`

Return the length of the key. If the algorithm supports multiple key lengths, the maximum supported value is returned. The length is returned as number of octets (bytes) and not as number of bits in

`nbytes`;`buffer`must be zero. Note that it is usually better to use the convenience function`gcry_cipher_get_algo_keylen`

.`GCRYCTL_GET_BLKLEN:`

Return the block length of the algorithm. The length is returned as a number of octets in

`nbytes`;`buffer`must be zero. Note that it is usually better to use the convenience function`gcry_cipher_get_algo_blklen`

.`GCRYCTL_TEST_ALGO:`

Returns

`0`

when the specified algorithm is available for use.`buffer`and`nbytes`must be zero.

- Function:
*size_t***gcry_cipher_get_algo_keylen***(*`algo`) -
This function returns length of the key for algorithm

`algo`. If the algorithm supports multiple key lengths, the maximum supported key length is returned. On error`0`

is returned. The key length is returned as number of octets.This is a convenience functions which should be preferred over

`gcry_cipher_algo_info`

because it allows for proper type checking.

- Function:
*size_t***gcry_cipher_get_algo_blklen***(int*`algo`) -
This functions returns the block-length of the algorithm

`algo`counted in octets. On error`0`

is returned.This is a convenience functions which should be preferred over

`gcry_cipher_algo_info`

because it allows for proper type checking.

- Function:
*const char ****gcry_cipher_algo_name***(int*`algo`) -
`gcry_cipher_algo_name`

returns a string with the name of the cipher algorithm`algo`. If the algorithm is not known or another error occurred, the string`"?"`

is returned. This function should not be used to test for the availability of an algorithm.

- Function:
*int***gcry_cipher_map_name***(const char **`name`) -
`gcry_cipher_map_name`

returns the algorithm identifier for the cipher algorithm described by the string`name`. If this algorithm is not available`0`

is returned.

- Function:
*int***gcry_cipher_mode_from_oid***(const char **`string`) -
Return the cipher mode associated with an ASN.1 object identifier. The object identifier is expected to be in the IETF-style dotted decimal notation. The function returns

`0`

for an unknown object identifier or when no mode is associated with it.

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