5 EVP_EncryptInit, EVP_EncryptUpdate, EVP_EncryptFinal - EVP cipher routines
9 #include <openssl/evp.h>
11 void EVP_EncryptInit(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type,
12 unsigned char *key, unsigned char *iv);
13 void EVP_EncryptUpdate(EVP_CIPHER_CTX *ctx, unsigned char *out,
14 int *outl, unsigned char *in, int inl);
15 void EVP_EncryptFinal(EVP_CIPHER_CTX *ctx, unsigned char *out,
18 void EVP_DecryptInit(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type,
19 unsigned char *key, unsigned char *iv);
20 void EVP_DecryptUpdate(EVP_CIPHER_CTX *ctx, unsigned char *out,
21 int *outl, unsigned char *in, int inl);
22 int EVP_DecryptFinal(EVP_CIPHER_CTX *ctx, unsigned char *outm,
25 void EVP_CipherInit(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type,
26 unsigned char *key, unsigned char *iv, int enc);
27 void EVP_CipherUpdate(EVP_CIPHER_CTX *ctx, unsigned char *out,
28 int *outl, unsigned char *in, int inl);
29 int EVP_CipherFinal(EVP_CIPHER_CTX *ctx, unsigned char *outm,
32 void EVP_CIPHER_CTX_cleanup(EVP_CIPHER_CTX *a);
34 const EVP_CIPHER *EVP_get_cipherbyname(const char *name);
35 #define EVP_get_cipherbynid(a) EVP_get_cipherbyname(OBJ_nid2sn(a))
36 #define EVP_get_cipherbyobj(a) EVP_get_cipherbynid(OBJ_obj2nid(a))
38 #define EVP_CIPHER_nid(e) ((e)->nid)
39 #define EVP_CIPHER_block_size(e) ((e)->block_size)
40 #define EVP_CIPHER_key_length(e) ((e)->key_len)
41 #define EVP_CIPHER_iv_length(e) ((e)->iv_len)
43 int EVP_CIPHER_type(const EVP_CIPHER *ctx);
44 #define EVP_CIPHER_CTX_cipher(e) ((e)->cipher)
45 #define EVP_CIPHER_CTX_nid(e) ((e)->cipher->nid)
46 #define EVP_CIPHER_CTX_block_size(e) ((e)->cipher->block_size)
47 #define EVP_CIPHER_CTX_key_length(e) ((e)->cipher->key_len)
48 #define EVP_CIPHER_CTX_iv_length(e) ((e)->cipher->iv_len)
49 #define EVP_CIPHER_CTX_type(c) EVP_CIPHER_type(EVP_CIPHER_CTX_cipher(c))
51 int EVP_CIPHER_param_to_asn1(EVP_CIPHER_CTX *c, ASN1_TYPE *type);
52 int EVP_CIPHER_asn1_to_param(EVP_CIPHER_CTX *c, ASN1_TYPE *type);
56 The EVP cipher routines are a high level interface to certain
59 EVP_EncryptInit() initialises a cipher context B<ctx> for encryption
60 with cipher B<type>. B<type> is normally supplied by a function such
61 as EVP_des_cbc() . B<key> is the symmetric key to use and B<iv> is the
62 IV to use (if necessary), the actual number of bytes used for the
63 key and IV depends on the cipher. It is possible to set all parameters
64 to NULL except B<type> in an initial call and supply the remaining
65 parameters in subsequent calls. This is normally done when the
66 EVP_CIPHER_asn1_to_param() function is called to set the cipher
67 parameters from an ASN1 AlgorithmIdentifier and the key from a
70 EVP_EncryptUpdate() encrypts B<inl> bytes from the buffer B<in> and
71 writes the encrypted version to B<out>. This function can be called
72 multiple times to encrypt successive blocks of data. The amount
73 of data written depends on the block alignment of the encrypted data:
74 as a result the amount of data written may be anything from zero bytes
75 to (inl + cipher_block_size - 1) so B<outl> should contain sufficient
76 room. The actual number of bytes written is placed in B<outl>.
78 EVP_EncryptFinal() encrypts the "final" data, that is any data that
79 remains in a partial block. It uses L<standard block padding|/NOTES> (aka PKCS
80 padding). The encrypted final data is written to B<out> which should
81 have sufficient space for one cipher block. The number of bytes written
82 is placed in B<outl>. After this function is called the encryption operation
83 is finished and no further calls to EVP_EncryptUpdate() should be made.
85 EVP_DecryptInit(), EVP_DecryptUpdate() and EVP_DecryptFinal() are the
86 corresponding decryption operations. EVP_DecryptFinal() will return an
87 error code if the final block is not correctly formatted. The parameters
88 and restrictions are identical to the encryption operations except that
89 the decrypted data buffer B<out> passed to EVP_DecryptUpdate() should
90 have sufficient room for (B<inl> + cipher_block_size) bytes unless the
91 cipher block size is 1 in which case B<inl> bytes is sufficient.
93 EVP_CipherInit(), EVP_CipherUpdate() and EVP_CipherFinal() are functions
94 that can be used for decryption or encryption. The operation performed
95 depends on the value of the B<enc> parameter. It should be set to 1 for
96 encryption and 0 for decryption.
98 EVP_CIPHER_CTX_cleanup() clears all information from a cipher context.
99 It should be called after all operations using a cipher are complete
100 so sensitive information does not remain in memory.
102 EVP_get_cipherbyname(), EVP_get_cipherbynid() and EVP_get_cipherbyobj()
103 return an EVP_CIPHER structure when passed a cipher name, a NID or an
104 ASN1_OBJECT structure.
106 EVP_CIPHER_nid() and EVP_CIPHER_CTX_nid() return the NID of a cipher when
107 passed an B<EVP_CIPHER> or B<EVP_CIPHER_CTX> structure. The actual NID
108 value is an internal value which may not have a corresponding OBJECT
111 EVP_CIPHER_key_length() and EVP_CIPHER_CTX_key_length() return the key
112 length of a cipher when passed an B<EVP_CIPHER> or B<EVP_CIPHER_CTX>
113 structure. The constant B<EVP_MAX_KEY_LENGTH> is the maximum key length
116 EVP_CIPHER_iv_length() and EVP_CIPHER_CTX_iv_length() return the IV
117 length of a cipher when passed an B<EVP_CIPHER> or B<EVP_CIPHER_CTX>.
118 It will return zero if the cipher does not use an IV. The constant
119 B<EVP_MAX_IV_LENGTH> is the maximum IV length for all ciphers.
121 EVP_CIPHER_block_size() and EVP_CIPHER_CTX_block_size() return the block
122 size of a cipher when passed an B<EVP_CIPHER> or B<EVP_CIPHER_CTX>
123 structure. The constant B<EVP_MAX_IV_LENGTH> is also the maximum block
124 length for all ciphers.
126 EVP_CIPHER_type() and EVP_CIPHER_CTX_type() return the type of the passed
127 cipher or context. This "type" is the actual NID of the cipher OBJECT
128 IDENTIFIER as such it ignores the cipher parameters and 40 bit RC2 and
129 128 bit RC2 have the same NID. If the cipher does not have an object
130 identifier or does not have ASN1 support this function will return
133 EVP_CIPHER_CTX_cipher() returns the B<EVP_CIPHER> structure when passed
134 an B<EVP_CIPHER_CTX> structure.
136 EVP_CIPHER_param_to_asn1() sets the AlgorithmIdentifier "parameter" based
137 on the passed cipher. This will typically include any parameters and an
138 IV. The cipher IV (if any) must be set when this call is made. This call
139 should be made before the cipher is actually "used" (before any
140 EVP_EncryptUpdate(), EVP_DecryptUpdate() calls for example). This function
141 may fail if the cipher does not have any ASN1 support.
143 EVP_CIPHER_asn1_to_param() sets the cipher parameters based on an ASN1
144 AlgorithmIdentifier "parameter". The precise effect depends on the cipher
145 In the case of RC2, for example, it will set the IV and effective key length.
146 This function should be called after the base cipher type is set but before
147 the key is set. For example EVP_CipherInit() will be called with the IV and
148 key set to NULL, EVP_CIPHER_asn1_to_param() will be called and finally
149 EVP_CipherInit() again with all parameters except the key set to NULL. It is
150 possible for this function to fail if the cipher does not have any ASN1 support
151 or the parameters cannot be set (for example the RC2 effective key length
152 does not have an B<EVP_CIPHER> structure).
156 EVP_EncryptInit(), EVP_EncryptUpdate() and EVP_EncryptFinal() do not return
159 EVP_DecryptInit() and EVP_DecryptUpdate() do not return values.
160 EVP_DecryptFinal() returns 0 if the decrypt failed or 1 for success.
162 EVP_CipherInit() and EVP_CipherUpdate() do not return values.
163 EVP_CipherFinal() returns 1 for a decryption failure or 1 for success, if
164 the operation is encryption then it always returns 1.
166 EVP_CIPHER_CTX_cleanup() does not return a value.
168 EVP_get_cipherbyname(), EVP_get_cipherbynid() and EVP_get_cipherbyobj()
169 return an B<EVP_CIPHER> structure or NULL on error.
171 EVP_CIPHER_nid() and EVP_CIPHER_CTX_nid() return a NID.
173 EVP_CIPHER_block_size() and EVP_CIPHER_CTX_block_size() return the block
176 EVP_CIPHER_key_length() and EVP_CIPHER_CTX_key_length() return the key
179 EVP_CIPHER_iv_length() and EVP_CIPHER_CTX_iv_length() return the IV
180 length or zero if the cipher does not use an IV.
182 EVP_CIPHER_type() and EVP_CIPHER_CTX_type() return the NID of the cipher's
183 OBJECT IDENTIFIER or NID_undef if it has no defined OBJECT IDENTIFIER.
185 EVP_CIPHER_CTX_cipher() returns an B<EVP_CIPHER> structure.
187 EVP_CIPHER_param_to_asn1() and EVP_CIPHER_asn1_to_param() return 1 for
188 success or zero for failure.
192 Where possible the B<EVP> interface to symmetric ciphers should be used in
193 preference to the low level interfaces. This is because the code then becomes
194 transparent to the cipher used and much more flexible.
196 PKCS padding works by adding B<n> padding bytes of value B<n> to make the total
197 length of the encrypted data a multiple of the block size. Padding is always
198 added so if the data is already a multiple of the block size B<n> will equal
199 the block size. For example if the block size is 8 and 11 bytes are to be
200 encrypted then 5 padding bytes of value 5 will be added.
202 When decrypting the final block is checked to see if it has the correct form.
204 Although the decryption operation can produce an error, it is not a strong
205 test that the input data or key is correct. A random block has better than
206 1 in 256 chance of being of the correct format and problems with the
207 input data earlier on will not produce a final decrypt error.
211 The current B<EVP> cipher interface is not as flexible as it should be. Only
212 certain "spot" encryption algorithms can be used for ciphers which have various
213 parameters associated with them (RC2, RC5 for example) this is inadequate.
215 Several of the functions do not return error codes because the software versions
216 can never fail. This is not true of hardware versions.