path: root/secure/lib/libcrypto/man/EVP_EncryptInit.3

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.IX Title "EVP_ENCRYPTINIT 1"
.TH EVP_ENCRYPTINIT 1 "perl v5.6.1" "2000-11-13" "User Contributed Perl Documentation"
.UC
.SH "NAME"
EVP_EncryptInit, EVP_EncryptUpdate, EVP_EncryptFinal, EVP_DecryptInit,
EVP_DecryptUpdate, EVP_DecryptFinal, EVP_CipherInit, EVP_CipherUpdate,
EVP_CipherFinal, EVP_CIPHER_CTX_set_key_length, EVP_CIPHER_CTX_ctrl,
EVP_CIPHER_CTX_cleanup, EVP_get_cipherbyname, EVP_get_cipherbynid,
EVP_get_cipherbyobj, EVP_CIPHER_nid, 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_nid,
EVP_CIPHER_CTX_block_size, EVP_CIPHER_CTX_key_length, EVP_CIPHER_CTX_iv_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 \- \s-1EVP\s0 cipher routines
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #include <openssl/evp.h>
.Ve
.Vb 6
\& int EVP_EncryptInit(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type,
\&         unsigned char *key, unsigned char *iv);
\& int EVP_EncryptUpdate(EVP_CIPHER_CTX *ctx, unsigned char *out,
\&         int *outl, unsigned char *in, int inl);
\& int EVP_EncryptFinal(EVP_CIPHER_CTX *ctx, unsigned char *out,
\&         int *outl);
.Ve
.Vb 6
\& int EVP_DecryptInit(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type,
\&         unsigned char *key, unsigned char *iv);
\& int EVP_DecryptUpdate(EVP_CIPHER_CTX *ctx, unsigned char *out,
\&         int *outl, unsigned char *in, int inl);
\& int EVP_DecryptFinal(EVP_CIPHER_CTX *ctx, unsigned char *outm,
\&         int *outl);
.Ve
.Vb 6
\& int EVP_CipherInit(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type,
\&         unsigned char *key, unsigned char *iv, int enc);
\& int EVP_CipherUpdate(EVP_CIPHER_CTX *ctx, unsigned char *out,
\&         int *outl, unsigned char *in, int inl);
\& int EVP_CipherFinal(EVP_CIPHER_CTX *ctx, unsigned char *outm,
\&         int *outl);
.Ve
.Vb 3
\& 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_cleanup(EVP_CIPHER_CTX *a);
.Ve
.Vb 3
\& const EVP_CIPHER *EVP_get_cipherbyname(const char *name);
\& #define EVP_get_cipherbynid(a) EVP_get_cipherbyname(OBJ_nid2sn(a))
\& #define EVP_get_cipherbyobj(a) EVP_get_cipherbynid(OBJ_obj2nid(a))
.Ve
.Vb 7
\& #define EVP_CIPHER_nid(e)              ((e)->nid)
\& #define EVP_CIPHER_block_size(e)       ((e)->block_size)
\& #define EVP_CIPHER_key_length(e)       ((e)->key_len)
\& #define EVP_CIPHER_iv_length(e)                ((e)->iv_len)
\& #define EVP_CIPHER_flags(e)            ((e)->flags)
\& #define EVP_CIPHER_mode(e)             ((e)->flags) & EVP_CIPH_MODE)
\& int EVP_CIPHER_type(const EVP_CIPHER *ctx);
.Ve
.Vb 10
\& #define EVP_CIPHER_CTX_cipher(e)       ((e)->cipher)
\& #define EVP_CIPHER_CTX_nid(e)          ((e)->cipher->nid)
\& #define EVP_CIPHER_CTX_block_size(e)   ((e)->cipher->block_size)
\& #define EVP_CIPHER_CTX_key_length(e)   ((e)->key_len)
\& #define EVP_CIPHER_CTX_iv_length(e)    ((e)->cipher->iv_len)
\& #define EVP_CIPHER_CTX_get_app_data(e) ((e)->app_data)
\& #define EVP_CIPHER_CTX_set_app_data(e,d) ((e)->app_data=(char *)(d))
\& #define EVP_CIPHER_CTX_type(c)         EVP_CIPHER_type(EVP_CIPHER_CTX_cipher(c))
\& #define EVP_CIPHER_CTX_flags(e)                ((e)->cipher->flags)
\& #define EVP_CIPHER_CTX_mode(e)         ((e)->cipher->flags & EVP_CIPH_MODE)
.Ve
.Vb 2
\& 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);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
The \s-1EVP\s0 cipher routines are a high level interface to certain
symmetric ciphers.
.PP
\&\fIEVP_EncryptInit()\fR initializes a cipher context \fBctx\fR for encryption
with cipher \fBtype\fR. \fBtype\fR is normally supplied by a function such
as \fIEVP_des_cbc()\fR . \fBkey\fR is the symmetric key to use and \fBiv\fR is the
\&\s-1IV\s0 to use (if necessary), the actual number of bytes used for the
key and \s-1IV\s0 depends on the cipher. It is possible to set all parameters
to \s-1NULL\s0 except \fBtype\fR in an initial call and supply the remaining
parameters in subsequent calls, all of which have \fBtype\fR set to \s-1NULL\s0.
This is done when the default cipher parameters are not appropriate.
.PP
\&\fIEVP_EncryptUpdate()\fR encrypts \fBinl\fR bytes from the buffer \fBin\fR and
writes the encrypted version to \fBout\fR. 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 \fBoutl\fR should contain sufficient
room.  The actual number of bytes written is placed in \fBoutl\fR.
.PP
\&\fIEVP_EncryptFinal()\fR encrypts the \*(L"final\*(R" data, that is any data that
remains in a partial block. It uses standard block padding (aka \s-1PKCS\s0
padding). The encrypted final data is written to \fBout\fR which should
have sufficient space for one cipher block. The number of bytes written
is placed in \fBoutl\fR. After this function is called the encryption operation
is finished and no further calls to \fIEVP_EncryptUpdate()\fR should be made.
.PP
\&\fIEVP_DecryptInit()\fR, \fIEVP_DecryptUpdate()\fR and \fIEVP_DecryptFinal()\fR are the
corresponding decryption operations. \fIEVP_DecryptFinal()\fR will return an
error code if the final block is not correctly formatted. The parameters
and restrictions are identical to the encryption operations except that
the decrypted data buffer \fBout\fR passed to \fIEVP_DecryptUpdate()\fR should
have sufficient room for (\fBinl\fR + cipher_block_size) bytes unless the
cipher block size is 1 in which case \fBinl\fR bytes is sufficient.
.PP
\&\fIEVP_CipherInit()\fR, \fIEVP_CipherUpdate()\fR and \fIEVP_CipherFinal()\fR are functions
that can be used for decryption or encryption. The operation performed
depends on the value of the \fBenc\fR 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).
.PP
\&\fIEVP_CIPHER_CTX_cleanup()\fR clears all information from a cipher context.
It should be called after all operations using a cipher are complete
so sensitive information does not remain in memory.
.PP
\&\fIEVP_get_cipherbyname()\fR, \fIEVP_get_cipherbynid()\fR and \fIEVP_get_cipherbyobj()\fR
return an \s-1EVP_CIPHER\s0 structure when passed a cipher name, a \s-1NID\s0 or an
\&\s-1ASN1_OBJECT\s0 structure.
.PP
\&\fIEVP_CIPHER_nid()\fR and \fIEVP_CIPHER_CTX_nid()\fR return the \s-1NID\s0 of a cipher when
passed an \fB\s-1EVP_CIPHER\s0\fR or \fB\s-1EVP_CIPHER_CTX\s0\fR structure.  The actual \s-1NID\s0
value is an internal value which may not have a corresponding \s-1OBJECT\s0
\&\s-1IDENTIFIER\s0.
.PP
\&\fIEVP_CIPHER_key_length()\fR and \fIEVP_CIPHER_CTX_key_length()\fR return the key
length of a cipher when passed an \fB\s-1EVP_CIPHER\s0\fR or \fB\s-1EVP_CIPHER_CTX\s0\fR
structure. The constant \fB\s-1EVP_MAX_KEY_LENGTH\s0\fR is the maximum key length
for all ciphers. Note: although \fIEVP_CIPHER_key_length()\fR is fixed for a
given cipher, the value of \fIEVP_CIPHER_CTX_key_length()\fR may be different
for variable key length ciphers.
.PP
\&\fIEVP_CIPHER_CTX_set_key_length()\fR 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.
.PP
\&\fIEVP_CIPHER_iv_length()\fR and \fIEVP_CIPHER_CTX_iv_length()\fR return the \s-1IV\s0
length of a cipher when passed an \fB\s-1EVP_CIPHER\s0\fR or \fB\s-1EVP_CIPHER_CTX\s0\fR.
It will return zero if the cipher does not use an \s-1IV\s0.  The constant
\&\fB\s-1EVP_MAX_IV_LENGTH\s0\fR is the maximum \s-1IV\s0 length for all ciphers.
.PP
\&\fIEVP_CIPHER_block_size()\fR and \fIEVP_CIPHER_CTX_block_size()\fR return the block
size of a cipher when passed an \fB\s-1EVP_CIPHER\s0\fR or \fB\s-1EVP_CIPHER_CTX\s0\fR
structure. The constant \fB\s-1EVP_MAX_IV_LENGTH\s0\fR is also the maximum block
length for all ciphers.
.PP
\&\fIEVP_CIPHER_type()\fR and \fIEVP_CIPHER_CTX_type()\fR return the type of the passed
cipher or context. This \*(L"type\*(R" is the actual \s-1NID\s0 of the cipher \s-1OBJECT\s0
\&\s-1IDENTIFIER\s0 as such it ignores the cipher parameters and 40 bit \s-1RC2\s0 and
128 bit \s-1RC2\s0 have the same \s-1NID\s0. If the cipher does not have an object
identifier or does not have \s-1ASN1\s0 support this function will return
\&\fBNID_undef\fR.
.PP
\&\fIEVP_CIPHER_CTX_cipher()\fR returns the \fB\s-1EVP_CIPHER\s0\fR structure when passed
an \fB\s-1EVP_CIPHER_CTX\s0\fR structure.
.PP
\&\fIEVP_CIPHER_mode()\fR and \fIEVP_CIPHER_CTX_mode()\fR return the block cipher mode:
\&\s-1EVP_CIPH_ECB_MODE\s0, \s-1EVP_CIPH_CBC_MODE\s0, \s-1EVP_CIPH_CFB_MODE\s0 or
\&\s-1EVP_CIPH_OFB_MODE\s0. If the cipher is a stream cipher then
\&\s-1EVP_CIPH_STREAM_CIPHER\s0 is returned.
.PP
\&\fIEVP_CIPHER_param_to_asn1()\fR sets the AlgorithmIdentifier \*(L"parameter\*(R" based
on the passed cipher. This will typically include any parameters and an
\&\s-1IV\s0. The cipher \s-1IV\s0 (if any) must be set when this call is made. This call
should be made before the cipher is actually \*(L"used\*(R" (before any
\&\fIEVP_EncryptUpdate()\fR, \fIEVP_DecryptUpdate()\fR calls for example). This function
may fail if the cipher does not have any \s-1ASN1\s0 support.
.PP
\&\fIEVP_CIPHER_asn1_to_param()\fR sets the cipher parameters based on an \s-1ASN1\s0
AlgorithmIdentifier \*(L"parameter\*(R". The precise effect depends on the cipher
In the case of \s-1RC2\s0, for example, it will set the \s-1IV\s0 and effective key length.
This function should be called after the base cipher type is set but before
the key is set. For example \fIEVP_CipherInit()\fR will be called with the \s-1IV\s0 and
key set to \s-1NULL\s0, \fIEVP_CIPHER_asn1_to_param()\fR will be called and finally
\&\fIEVP_CipherInit()\fR again with all parameters except the key set to \s-1NULL\s0. It is
possible for this function to fail if the cipher does not have any \s-1ASN1\s0 support
or the parameters cannot be set (for example the \s-1RC2\s0 effective key length
is not supported.
.PP
\&\fIEVP_CIPHER_CTX_ctrl()\fR allows various cipher specific parameters to be determined
and set. Currently only the \s-1RC2\s0 effective key length and the number of rounds of
\&\s-1RC5\s0 can be set.
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
\&\fIEVP_EncryptInit()\fR, \fIEVP_EncryptUpdate()\fR and \fIEVP_EncryptFinal()\fR return 1 for success
and 0 for failure.
.PP
\&\fIEVP_DecryptInit()\fR and \fIEVP_DecryptUpdate()\fR return 1 for success and 0 for failure.
\&\fIEVP_DecryptFinal()\fR returns 0 if the decrypt failed or 1 for success.
.PP
\&\fIEVP_CipherInit()\fR and \fIEVP_CipherUpdate()\fR return 1 for success and 0 for failure.
\&\fIEVP_CipherFinal()\fR returns 1 for a decryption failure or 1 for success.
.PP
\&\fIEVP_CIPHER_CTX_cleanup()\fR returns 1 for success and 0 for failure.
.PP
\&\fIEVP_get_cipherbyname()\fR, \fIEVP_get_cipherbynid()\fR and \fIEVP_get_cipherbyobj()\fR
return an \fB\s-1EVP_CIPHER\s0\fR structure or \s-1NULL\s0 on error.
.PP
\&\fIEVP_CIPHER_nid()\fR and \fIEVP_CIPHER_CTX_nid()\fR return a \s-1NID\s0.
.PP
\&\fIEVP_CIPHER_block_size()\fR and \fIEVP_CIPHER_CTX_block_size()\fR return the block
size.
.PP
\&\fIEVP_CIPHER_key_length()\fR and \fIEVP_CIPHER_CTX_key_length()\fR return the key
length.
.PP
\&\fIEVP_CIPHER_iv_length()\fR and \fIEVP_CIPHER_CTX_iv_length()\fR return the \s-1IV\s0
length or zero if the cipher does not use an \s-1IV\s0.
.PP
\&\fIEVP_CIPHER_type()\fR and \fIEVP_CIPHER_CTX_type()\fR return the \s-1NID\s0 of the cipher's
\&\s-1OBJECT\s0 \s-1IDENTIFIER\s0 or NID_undef if it has no defined \s-1OBJECT\s0 \s-1IDENTIFIER\s0.
.PP
\&\fIEVP_CIPHER_CTX_cipher()\fR returns an \fB\s-1EVP_CIPHER\s0\fR structure.
.PP
\&\fIEVP_CIPHER_param_to_asn1()\fR and \fIEVP_CIPHER_asn1_to_param()\fR return 1 for 
success or zero for failure.
.SH "CIPHER LISTING"
.IX Header "CIPHER LISTING"
All algorithms have a fixed key length unless otherwise stated.
.Ip "\fIEVP_enc_null()\fR" 4
.IX Item "EVP_enc_null()"
Null cipher: does nothing.
.Ip "EVP_des_cbc(void), EVP_des_ecb(void), EVP_des_cfb(void), EVP_des_ofb(void)" 4
.IX Item "EVP_des_cbc(void), EVP_des_ecb(void), EVP_des_cfb(void), EVP_des_ofb(void)"
\&\s-1DES\s0 in \s-1CBC\s0, \s-1ECB\s0, \s-1CFB\s0 and \s-1OFB\s0 modes respectively. 
.Ip "EVP_des_ede_cbc(void), \fIEVP_des_ede()\fR, EVP_des_ede_ofb(void),  EVP_des_ede_cfb(void)" 4
.IX Item "EVP_des_ede_cbc(void), EVP_des_ede(), EVP_des_ede_ofb(void),  EVP_des_ede_cfb(void)"
Two key triple \s-1DES\s0 in \s-1CBC\s0, \s-1ECB\s0, \s-1CFB\s0 and \s-1OFB\s0 modes respectively.
.Ip "EVP_des_ede3_cbc(void), \fIEVP_des_ede3()\fR, EVP_des_ede3_ofb(void),  EVP_des_ede3_cfb(void)" 4
.IX Item "EVP_des_ede3_cbc(void), EVP_des_ede3(), EVP_des_ede3_ofb(void),  EVP_des_ede3_cfb(void)"
Three key triple \s-1DES\s0 in \s-1CBC\s0, \s-1ECB\s0, \s-1CFB\s0 and \s-1OFB\s0 modes respectively.
.Ip "EVP_desx_cbc(void)" 4
.IX Item "EVP_desx_cbc(void)"
\&\s-1DESX\s0 algorithm in \s-1CBC\s0 mode.
.Ip "EVP_rc4(void)" 4
.IX Item "EVP_rc4(void)"
\&\s-1RC4\s0 stream cipher. This is a variable key length cipher with default key length 128 bits.
.Ip "EVP_rc4_40(void)" 4
.IX Item "EVP_rc4_40(void)"
\&\s-1RC4\s0 stream cipher with 40 bit key length. This is obsolete and new code should use \fIEVP_rc4()\fR
and the \fIEVP_CIPHER_CTX_set_key_length()\fR function.
.Ip "\fIEVP_idea_cbc()\fR EVP_idea_ecb(void), EVP_idea_cfb(void), EVP_idea_ofb(void), EVP_idea_cbc(void)" 4
.IX Item "EVP_idea_cbc() EVP_idea_ecb(void), EVP_idea_cfb(void), EVP_idea_ofb(void), EVP_idea_cbc(void)"
\&\s-1IDEA\s0 encryption algorithm in \s-1CBC\s0, \s-1ECB\s0, \s-1CFB\s0 and \s-1OFB\s0 modes respectively.
.Ip "EVP_rc2_cbc(void), EVP_rc2_ecb(void), EVP_rc2_cfb(void), EVP_rc2_ofb(void)" 4
.IX Item "EVP_rc2_cbc(void), EVP_rc2_ecb(void), EVP_rc2_cfb(void), EVP_rc2_ofb(void)"
\&\s-1RC2\s0 encryption algorithm in \s-1CBC\s0, \s-1ECB\s0, \s-1CFB\s0 and \s-1OFB\s0 modes respectively. This is a variable key
length cipher with an additional parameter called \*(L"effective key bits\*(R" or \*(L"effective key length\*(R".
By default both are set to 128 bits.
.Ip "EVP_rc2_40_cbc(void), EVP_rc2_64_cbc(void)" 4
.IX Item "EVP_rc2_40_cbc(void), EVP_rc2_64_cbc(void)"
\&\s-1RC2\s0 algorithm in \s-1CBC\s0 mode with a default key length and effective key length of 40 and 64 bits.
These are obsolete and new code should use \fIEVP_rc2_cbc()\fR, \fIEVP_CIPHER_CTX_set_key_length()\fR and
\&\fIEVP_CIPHER_CTX_ctrl()\fR to set the key length and effective key length.
.Ip "EVP_bf_cbc(void), EVP_bf_ecb(void), EVP_bf_cfb(void), EVP_bf_ofb(void);" 4
.IX Item "EVP_bf_cbc(void), EVP_bf_ecb(void), EVP_bf_cfb(void), EVP_bf_ofb(void);"
Blowfish encryption algorithm in \s-1CBC\s0, \s-1ECB\s0, \s-1CFB\s0 and \s-1OFB\s0 modes respectively. This is a variable key
length cipher.
.Ip "EVP_cast5_cbc(void), EVP_cast5_ecb(void), EVP_cast5_cfb(void), EVP_cast5_ofb(void)" 4
.IX Item "EVP_cast5_cbc(void), EVP_cast5_ecb(void), EVP_cast5_cfb(void), EVP_cast5_ofb(void)"
\&\s-1CAST\s0 encryption algorithm in \s-1CBC\s0, \s-1ECB\s0, \s-1CFB\s0 and \s-1OFB\s0 modes respectively. This is a variable key
length cipher.
.Ip "EVP_rc5_32_12_16_cbc(void), EVP_rc5_32_12_16_ecb(void), EVP_rc5_32_12_16_cfb(void), EVP_rc5_32_12_16_ofb(void)" 4
.IX Item "EVP_rc5_32_12_16_cbc(void), EVP_rc5_32_12_16_ecb(void), EVP_rc5_32_12_16_cfb(void), EVP_rc5_32_12_16_ofb(void)"
\&\s-1RC5\s0 encryption algorithm in \s-1CBC\s0, \s-1ECB\s0, \s-1CFB\s0 and \s-1OFB\s0 modes respectively. This is a variable key length
cipher with an additional \*(L"number of rounds\*(R" parameter. By default the key length is set to 128
bits and 12 rounds.
.SH "NOTES"
.IX Header "NOTES"
Where possible the \fB\s-1EVP\s0\fR 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.
.PP
\&\s-1PKCS\s0 padding works by adding \fBn\fR padding bytes of value \fBn\fR 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 \fBn\fR 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.
.PP
When decrypting the final block is checked to see if it has the correct form.
.PP
Although the decryption operation can produce an error, 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.
.PP
The functions \fIEVP_EncryptInit()\fR, \fIEVP_EncryptUpdate()\fR, \fIEVP_EncryptFinal()\fR,
\&\fIEVP_DecryptInit()\fR, \fIEVP_DecryptUpdate()\fR, \fIEVP_CipherInit()\fR and \fIEVP_CipherUpdate()\fR
and \fIEVP_CIPHER_CTX_cleanup()\fR did not return errors in OpenSSL version 0.9.5a or
earlier. Software only versions of encryption algorithms will never return
error codes for these functions, unless there is a programming error (for example
and attempt to set the key before the cipher is set in \fIEVP_EncryptInit()\fR ).
.SH "BUGS"
.IX Header "BUGS"
For \s-1RC5\s0 the number of rounds can currently only be set to 8, 12 or 16. This is
a limitation of the current \s-1RC5\s0 code rather than the \s-1EVP\s0 interface.
.PP
It should be possible to disable \s-1PKCS\s0 padding: currently it isn't.
.PP
\&\s-1EVP_MAX_KEY_LENGTH\s0 and \s-1EVP_MAX_IV_LENGTH\s0 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 \s-1EVP_MAX_KEY_LENGTH\s0 bytes.
.PP
The \s-1ASN1\s0 code is incomplete (and sometimes inaccurate) it has only been tested
for certain common S/MIME ciphers (\s-1RC2\s0, \s-1DES\s0, triple \s-1DES\s0) in \s-1CBC\s0 mode.
.SH "EXAMPLES"
.IX Header "EXAMPLES"
Get the number of rounds used in \s-1RC5:\s0
.PP
.Vb 2
\& int nrounds;
\& EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GET_RC5_ROUNDS, 0, &i);
.Ve
Get the \s-1RC2\s0 effective key length:
.PP
.Vb 2
\& int key_bits;
\& EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GET_RC2_KEY_BITS, 0, &i);
.Ve
Set the number of rounds used in \s-1RC5:\s0
.PP
.Vb 2
\& int nrounds;
\& EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_SET_RC5_ROUNDS, i, NULL);
.Ve
Set the number of rounds used in \s-1RC2:\s0
.PP
.Vb 2
\& int nrounds;
\& EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_SET_RC2_KEY_BITS, i, NULL);
.Ve
.SH "SEE ALSO"
.IX Header "SEE ALSO"
evp(3)
.SH "HISTORY"
.IX Header "HISTORY"