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.\"
.IX Title "EVP_EncryptInit 3"
.TH EVP_EncryptInit 3 "2026-02-10" "1.0.2k" "OpenSSL"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
EVP_CIPHER_CTX_init, 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_CIPHER_CTX_cleanup, EVP_EncryptInit,
EVP_EncryptFinal, EVP_DecryptInit, EVP_DecryptFinal,
EVP_CipherInit, EVP_CipherFinal, 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,
EVP_CIPHER_CTX_set_padding,  EVP_enc_null, EVP_des_cbc, EVP_des_ecb,
EVP_des_cfb, EVP_des_ofb, EVP_des_ede_cbc, EVP_des_ede, EVP_des_ede_ofb,
EVP_des_ede_cfb, EVP_des_ede3_cbc, EVP_des_ede3, EVP_des_ede3_ofb,
EVP_des_ede3_cfb, EVP_desx_cbc, EVP_rc4, EVP_rc4_40, EVP_idea_cbc,
EVP_idea_ecb, EVP_idea_cfb, EVP_idea_ofb, EVP_idea_cbc, EVP_rc2_cbc,
EVP_rc2_ecb, EVP_rc2_cfb, EVP_rc2_ofb, EVP_rc2_40_cbc, EVP_rc2_64_cbc,
EVP_bf_cbc, EVP_bf_ecb, EVP_bf_cfb, EVP_bf_ofb, EVP_cast5_cbc,
EVP_cast5_ecb, EVP_cast5_cfb, EVP_cast5_ofb, EVP_rc5_32_12_16_cbc,
EVP_rc5_32_12_16_ecb, EVP_rc5_32_12_16_cfb, EVP_rc5_32_12_16_ofb, 
EVP_aes_128_gcm, EVP_aes_192_gcm, EVP_aes_256_gcm, EVP_aes_128_ccm,
EVP_aes_192_ccm, EVP_aes_256_ccm \- EVP cipher routines
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #include <openssl/evp.h>
\&
\& void EVP_CIPHER_CTX_init(EVP_CIPHER_CTX *a);
\&
\& int EVP_EncryptInit_ex(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type,
\&         ENGINE *impl, 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_ex(EVP_CIPHER_CTX *ctx, unsigned char *out,
\&         int *outl);
\&
\& int EVP_DecryptInit_ex(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type,
\&         ENGINE *impl, 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_ex(EVP_CIPHER_CTX *ctx, unsigned char *outm,
\&         int *outl);
\&
\& int EVP_CipherInit_ex(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type,
\&         ENGINE *impl, 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_ex(EVP_CIPHER_CTX *ctx, unsigned char *outm,
\&         int *outl);
\&
\& int EVP_EncryptInit(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type,
\&         unsigned char *key, 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,
\&         unsigned char *key, 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,
\&         unsigned char *key, unsigned char *iv, int enc);
\& int EVP_CipherFinal(EVP_CIPHER_CTX *ctx, unsigned char *outm,
\&         int *outl);
\&
\& 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_cleanup(EVP_CIPHER_CTX *a);
\&
\& 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))
\&
\& #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);
\&
\& #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)
\&
\& 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);
\&
\& const EVP_CIPHER *EVP_des_ede3(void);
\& const EVP_CIPHER *EVP_des_ede3_ecb(void);
\& const EVP_CIPHER *EVP_des_ede3_cfb64(void);
\& const EVP_CIPHER *EVP_des_ede3_cfb1(void);
\& const EVP_CIPHER *EVP_des_ede3_cfb8(void);
\& const EVP_CIPHER *EVP_des_ede3_ofb(void);
\& const EVP_CIPHER *EVP_des_ede3_cbc(void);
\& const EVP_CIPHER *EVP_aes_128_ecb(void);
\& const EVP_CIPHER *EVP_aes_128_cbc(void);
\& const EVP_CIPHER *EVP_aes_128_cfb1(void);
\& const EVP_CIPHER *EVP_aes_128_cfb8(void);
\& const EVP_CIPHER *EVP_aes_128_cfb128(void);
\& const EVP_CIPHER *EVP_aes_128_ofb(void);
\& const EVP_CIPHER *EVP_aes_192_ecb(void);
\& const EVP_CIPHER *EVP_aes_192_cbc(void);
\& const EVP_CIPHER *EVP_aes_192_cfb1(void);
\& const EVP_CIPHER *EVP_aes_192_cfb8(void);
\& const EVP_CIPHER *EVP_aes_192_cfb128(void);
\& const EVP_CIPHER *EVP_aes_192_ofb(void);
\& const EVP_CIPHER *EVP_aes_256_ecb(void);
\& const EVP_CIPHER *EVP_aes_256_cbc(void);
\& const EVP_CIPHER *EVP_aes_256_cfb1(void);
\& const EVP_CIPHER *EVP_aes_256_cfb8(void);
\& const EVP_CIPHER *EVP_aes_256_cfb128(void);
\& const EVP_CIPHER *EVP_aes_256_ofb(void);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
The \s-1EVP\s0 cipher routines are a high level interface to certain
symmetric ciphers.
.PP
\&\fIEVP_CIPHER_CTX_init()\fR initializes cipher contex \fBctx\fR.
.PP
\&\fIEVP_EncryptInit_ex()\fR sets up cipher context \fBctx\fR for encryption
with cipher \fBtype\fR from \s-1ENGINE \s0\fBimpl\fR. \fBctx\fR must be initialized
before calling this function. \fBtype\fR is normally supplied
by a function such as \fIEVP_aes_256_cbc()\fR. If \fBimpl\fR is \s-1NULL\s0 then the
default implementation is used. \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 \fBout\fR should contain sufficient
room. The actual number of bytes written is placed in \fBoutl\fR.
.PP
If padding is enabled (the default) then \fIEVP_EncryptFinal_ex()\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
If padding is disabled then \fIEVP_EncryptFinal_ex()\fR 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.
.PP
\&\fIEVP_DecryptInit_ex()\fR, \fIEVP_DecryptUpdate()\fR and \fIEVP_DecryptFinal_ex()\fR are the
corresponding decryption operations. \fIEVP_DecryptFinal()\fR 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 \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_ex()\fR, \fIEVP_CipherUpdate()\fR and \fIEVP_CipherFinal_ex()\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
and free up any allocated memory associate with it. It should be called
after all operations using a cipher are complete so sensitive information
does not remain in memory.
.PP
\&\fIEVP_EncryptInit()\fR, \fIEVP_DecryptInit()\fR and \fIEVP_CipherInit()\fR behave in a
similar way to \fIEVP_EncryptInit_ex()\fR, EVP_DecryptInit_ex and
\&\fIEVP_CipherInit_ex()\fR except the \fBctx\fR parameter does not need to be
initialized and they always use the default cipher implementation.
.PP
\&\fIEVP_EncryptFinal()\fR, \fIEVP_DecryptFinal()\fR and \fIEVP_CipherFinal()\fR are
identical to \fIEVP_EncryptFinal_ex()\fR, \fIEVP_DecryptFinal_ex()\fR and
\&\fIEVP_CipherFinal_ex()\fR. In previous releases they also cleaned up
the \fBctx\fR, but this is no longer done and \fIEVP_CIPHER_CTX_clean()\fR
must be called to free any context resources.
.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
IDENTIFIER.\s0
.PP
\&\fIEVP_CIPHER_CTX_set_padding()\fR enables or disables padding. By default
encryption operations are padded using standard block padding and the
padding is checked and removed when decrypting. If the \fBpad\fR 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.
.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
IDENTIFIER\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, EVP_CIPH_CBC_MODE, EVP_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.
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
\&\fIEVP_EncryptInit_ex()\fR, \fIEVP_EncryptUpdate()\fR and \fIEVP_EncryptFinal_ex()\fR
return 1 for success and 0 for failure.
.PP
\&\fIEVP_DecryptInit_ex()\fR and \fIEVP_DecryptUpdate()\fR return 1 for success and 0 for failure.
\&\fIEVP_DecryptFinal_ex()\fR returns 0 if the decrypt failed or 1 for success.
.PP
\&\fIEVP_CipherInit_ex()\fR and \fIEVP_CipherUpdate()\fR return 1 for success and 0 for failure.
\&\fIEVP_CipherFinal_ex()\fR returns 0 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_CTX_set_padding()\fR always returns 1.
.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 IDENTIFIER\s0 or NID_undef if it has no defined \s-1OBJECT IDENTIFIER.\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, ECB, CFB\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, ECB, CFB\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, ECB, CFB\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_aes_128_cbc(void), \fIEVP_aes_128_ecb()\fR, EVP_aes_128_ofb(void), EVP_aes_128_cfb1(void), EVP_aes_128_cfb8(void), EVP_aes_128_cfb128(void)" 4
.IX Item "EVP_aes_128_cbc(void), EVP_aes_128_ecb(), EVP_aes_128_ofb(void), EVP_aes_128_cfb1(void), EVP_aes_128_cfb8(void), EVP_aes_128_cfb128(void)"
\&\s-1AES\s0 with 128 bit key length in \s-1CBC, ECB, OFB\s0 and \s-1CFB\s0 modes respectively.
.IP "EVP_aes_192_cbc(void), \fIEVP_aes_192_ecb()\fR, EVP_aes_192_ofb(void), EVP_aes_192_cfb1(void), EVP_aes_192_cfb8(void), EVP_aes_192_cfb128(void)" 4
.IX Item "EVP_aes_192_cbc(void), EVP_aes_192_ecb(), EVP_aes_192_ofb(void), EVP_aes_192_cfb1(void), EVP_aes_192_cfb8(void), EVP_aes_192_cfb128(void)"
\&\s-1AES\s0 with 192 bit key length in \s-1CBC, ECB, OFB\s0 and \s-1CFB\s0 modes respectively.
.IP "EVP_aes_256_cbc(void), \fIEVP_aes_256_ecb()\fR, EVP_aes_256_ofb(void), EVP_aes_256_cfb1(void), EVP_aes_256_cfb8(void), EVP_aes_256_cfb128(void)" 4
.IX Item "EVP_aes_256_cbc(void), EVP_aes_256_ecb(), EVP_aes_256_ofb(void), EVP_aes_256_cfb1(void), EVP_aes_256_cfb8(void), EVP_aes_256_cfb128(void)"
\&\s-1AES\s0 with 256 bit key length in \s-1CBC, ECB, OFB\s0 and \s-1CFB\s0 modes respectively.
.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, ECB, CFB\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, ECB, CFB\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, ECB, CFB\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, ECB, CFB\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, ECB, CFB\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.
.IP "EVP_aes_128_gcm(void), EVP_aes_192_gcm(void), EVP_aes_256_gcm(void)" 4
.IX Item "EVP_aes_128_gcm(void), EVP_aes_192_gcm(void), EVP_aes_256_gcm(void)"
\&\s-1AES\s0 Galois Counter Mode (\s-1GCM\s0) for 128, 192 and 256 bit keys respectively.
These ciphers require additional control operations to function correctly: see
\&\*(L"\s-1GCM\s0 mode\*(R" section below for details.
.IP "EVP_aes_128_ccm(void), EVP_aes_192_ccm(void), EVP_aes_256_ccm(void)" 4
.IX Item "EVP_aes_128_ccm(void), EVP_aes_192_ccm(void), EVP_aes_256_ccm(void)"
\&\s-1AES\s0 Counter with CBC-MAC Mode (\s-1CCM\s0) for 128, 192 and 256 bit keys respectively.
These ciphers require additional control operations to function correctly: see
\&\s-1CCM\s0 mode section below for details.
.SH "GCM Mode"
.IX Header "GCM Mode"
For \s-1GCM\s0 mode ciphers the behaviour of the \s-1EVP\s0 interface is subtly altered and
several \s-1GCM\s0 specific ctrl operations are supported.
.PP
To specify any additional authenticated data (\s-1AAD\s0) a call to \fIEVP_CipherUpdate()\fR,
\&\fIEVP_EncryptUpdate()\fR or \fIEVP_DecryptUpdate()\fR should be made with the output 
parameter \fBout\fR set to \fB\s-1NULL\s0\fR.
.PP
When decrypting the return value of \fIEVP_DecryptFinal()\fR or \fIEVP_CipherFinal()\fR
indicates if the operation was successful. If it does not indicate success
the authentication operation has failed and any output data \fB\s-1MUST NOT\s0\fR
be used as it is corrupted.
.PP
The following ctrls are supported in \s-1GCM\s0 mode:
.PP
.Vb 1
\& EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_IVLEN, ivlen, NULL);
.Ve
.PP
Sets the \s-1GCM IV\s0 length: this call can only be made before specifying an \s-1IV.\s0 If
not called a default \s-1IV\s0 length is used (96 bits for \s-1AES\s0).
.PP
.Vb 1
\& EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_GET_TAG, taglen, tag);
.Ve
.PP
Writes \fBtaglen\fR bytes of the tag value to the buffer indicated by \fBtag\fR.
This call can only be made when encrypting data and \fBafter\fR all data has been
processed (e.g. after an \fIEVP_EncryptFinal()\fR call).
.PP
.Vb 1
\& EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_TAG, taglen, tag);
.Ve
.PP
Sets the expected tag to \fBtaglen\fR bytes from \fBtag\fR. This call is only legal
when decrypting data and must be made \fBbefore\fR any data is processed (e.g.
before any \fIEVP_DecryptUpdate()\fR call).
.PP
See \s-1EXAMPLES\s0 below for an example of the use of \s-1GCM\s0 mode.
.SH "CCM Mode"
.IX Header "CCM Mode"
The behaviour of \s-1CCM\s0 mode ciphers is similar to \s-1CCM\s0 mode but with a few
additional requirements and different ctrl values.
.PP
Like \s-1GCM\s0 mode any additional authenticated data (\s-1AAD\s0) is passed by calling
\&\fIEVP_CipherUpdate()\fR, \fIEVP_EncryptUpdate()\fR or \fIEVP_DecryptUpdate()\fR with the output 
parameter \fBout\fR set to \fB\s-1NULL\s0\fR. Additionally the total plaintext or ciphertext
length \fB\s-1MUST\s0\fR be passed to \fIEVP_CipherUpdate()\fR, \fIEVP_EncryptUpdate()\fR or
\&\fIEVP_DecryptUpdate()\fR with the output and input parameters (\fBin\fR and \fBout\fR) 
set to \fB\s-1NULL\s0\fR and the length passed in the \fBinl\fR parameter.
.PP
The following ctrls are supported in \s-1CCM\s0 mode:
.PP
.Vb 1
\& EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_CCM_SET_TAG, taglen, tag);
.Ve
.PP
This call is made to set the expected \fB\s-1CCM\s0\fR tag value when decrypting or
the length of the tag (with the \fBtag\fR parameter set to \s-1NULL\s0) when encrypting.
The tag length is often referred to as \fBM\fR. If not set a default value is
used (12 for \s-1AES\s0).
.PP
.Vb 1
\& EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_CCM_SET_L, ivlen, NULL);
.Ve
.PP
Sets the \s-1CCM \s0\fBL\fR value. If not set a default is used (8 for \s-1AES\s0).
.PP
.Vb 1
\& EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_CCM_SET_IVLEN, ivlen, NULL);
.Ve
.PP
Sets the \s-1CCM\s0 nonce (\s-1IV\s0) length: this call can only be made before specifying
an nonce value. The nonce length is given by \fB15 \- L\fR so it is 7 by default
for \s-1AES.\s0
.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. Additionally, the
\&\fB\s-1EVP\s0\fR interface will ensure the use of platform specific cryptographic
acceleration such as AES-NI (the low level interfaces do not provide the
guarantee).
.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 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.
.PP
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.
.PP
The functions \fIEVP_EncryptInit()\fR, \fIEVP_EncryptFinal()\fR, \fIEVP_DecryptInit()\fR,
\&\fIEVP_CipherInit()\fR and \fIEVP_CipherFinal()\fR are obsolete but are retained for
compatibility with existing code. New code should use \fIEVP_EncryptInit_ex()\fR,
\&\fIEVP_EncryptFinal_ex()\fR, \fIEVP_DecryptInit_ex()\fR, \fIEVP_DecryptFinal_ex()\fR,
\&\fIEVP_CipherInit_ex()\fR and \fIEVP_CipherFinal_ex()\fR because they can reuse an
existing context without allocating and freeing it up on each call.
.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
\&\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, DES,\s0 triple \s-1DES\s0) in \s-1CBC\s0 mode.
.SH "EXAMPLES"
.IX Header "EXAMPLES"
Encrypt a string using \s-1IDEA:\s0
.PP
.Vb 12
\& int do_crypt(char *outfile)
\&        {
\&        unsigned char outbuf[1024];
\&        int outlen, tmplen;
\&        /* Bogus key and IV: we\*(Aqd 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;
\&
\&        EVP_CIPHER_CTX_init(&ctx);
\&        EVP_EncryptInit_ex(&ctx, EVP_idea_cbc(), NULL, key, iv);
\&
\&        if(!EVP_EncryptUpdate(&ctx, outbuf, &outlen, intext, strlen(intext)))
\&                {
\&                /* Error */
\&                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 */
\&                return 0;
\&                }
\&        outlen += tmplen;
\&        EVP_CIPHER_CTX_cleanup(&ctx);
\&        /* Need binary mode for fopen because encrypted data is
\&         * binary data. Also cannot use strlen() on it because
\&         * it wont be null terminated and may contain embedded
\&         * nulls.
\&         */
\&        out = fopen(outfile, "wb");
\&        fwrite(outbuf, 1, outlen, out);
\&        fclose(out);
\&        return 1;
\&        }
.Ve
.PP
The ciphertext from the above example can be decrypted using the \fBopenssl\fR
utility with the command line (shown on two lines for clarity):
.PP
.Vb 2
\& openssl idea \-d <filename
\&          \-K 000102030405060708090A0B0C0D0E0F \-iv 0102030405060708
.Ve
.PP
General encryption and decryption function example using \s-1FILE I/O\s0 and \s-1AES128\s0
with a 128\-bit key:
.PP
.Vb 11
\& 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\*(Aqd normally set these from
\&         * another source.
\&         */
\&        unsigned char key[] = "0123456789abcdeF";
\&        unsigned char iv[] = "1234567887654321";
\&
\&        /* Don\*(Aqt set key or IV right away; we want to check lengths */
\&        EVP_CIPHER_CTX_init(&ctx);
\&        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_cleanup(&ctx);
\&                        return 0;
\&                        }
\&                fwrite(outbuf, 1, outlen, out);
\&                }
\&        if(!EVP_CipherFinal_ex(&ctx, outbuf, &outlen))
\&                {
\&                /* Error */
\&                EVP_CIPHER_CTX_cleanup(&ctx);
\&                return 0;
\&                }
\&        fwrite(outbuf, 1, outlen, out);
\&
\&        EVP_CIPHER_CTX_cleanup(&ctx);
\&        return 1;
\&        }
.Ve
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fIevp\fR\|(3)
.SH "HISTORY"
.IX Header "HISTORY"
\&\fIEVP_CIPHER_CTX_init()\fR, \fIEVP_EncryptInit_ex()\fR, \fIEVP_EncryptFinal_ex()\fR,
\&\fIEVP_DecryptInit_ex()\fR, \fIEVP_DecryptFinal_ex()\fR, \fIEVP_CipherInit_ex()\fR,
\&\fIEVP_CipherFinal_ex()\fR and \fIEVP_CIPHER_CTX_set_padding()\fR appeared in
OpenSSL 0.9.7.
.PP
\&\s-1IDEA\s0 appeared in OpenSSL 0.9.7 but was often disabled due to
patent concerns; the last patents expired in 2012.
