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https://github.com/openssl/openssl.git
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225 lines
9.8 KiB
Plaintext
225 lines
9.8 KiB
Plaintext
=pod
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=head1 NAME
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EVP_EncryptInit, EVP_EncryptUpdate, EVP_EncryptFinal - EVP cipher routines
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=head1 SYNOPSIS
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#include <openssl/evp.h>
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void EVP_EncryptInit(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type,
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unsigned char *key, unsigned char *iv);
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void EVP_EncryptUpdate(EVP_CIPHER_CTX *ctx, unsigned char *out,
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int *outl, unsigned char *in, int inl);
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void EVP_EncryptFinal(EVP_CIPHER_CTX *ctx, unsigned char *out,
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int *outl);
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void EVP_DecryptInit(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type,
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unsigned char *key, unsigned char *iv);
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void EVP_DecryptUpdate(EVP_CIPHER_CTX *ctx, unsigned char *out,
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int *outl, unsigned char *in, int inl);
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int EVP_DecryptFinal(EVP_CIPHER_CTX *ctx, unsigned char *outm,
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int *outl);
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void EVP_CipherInit(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type,
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unsigned char *key, unsigned char *iv, int enc);
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void EVP_CipherUpdate(EVP_CIPHER_CTX *ctx, unsigned char *out,
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int *outl, unsigned char *in, int inl);
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int EVP_CipherFinal(EVP_CIPHER_CTX *ctx, unsigned char *outm,
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int *outl);
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void EVP_CIPHER_CTX_cleanup(EVP_CIPHER_CTX *a);
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const EVP_CIPHER *EVP_get_cipherbyname(const char *name);
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#define EVP_get_cipherbynid(a) EVP_get_cipherbyname(OBJ_nid2sn(a))
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#define EVP_get_cipherbyobj(a) EVP_get_cipherbynid(OBJ_obj2nid(a))
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#define EVP_CIPHER_nid(e) ((e)->nid)
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#define EVP_CIPHER_block_size(e) ((e)->block_size)
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#define EVP_CIPHER_key_length(e) ((e)->key_len)
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#define EVP_CIPHER_iv_length(e) ((e)->iv_len)
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int EVP_CIPHER_type(const EVP_CIPHER *ctx);
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#define EVP_CIPHER_CTX_cipher(e) ((e)->cipher)
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#define EVP_CIPHER_CTX_nid(e) ((e)->cipher->nid)
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#define EVP_CIPHER_CTX_block_size(e) ((e)->cipher->block_size)
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#define EVP_CIPHER_CTX_key_length(e) ((e)->cipher->key_len)
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#define EVP_CIPHER_CTX_iv_length(e) ((e)->cipher->iv_len)
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#define EVP_CIPHER_CTX_type(c) EVP_CIPHER_type(EVP_CIPHER_CTX_cipher(c))
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int EVP_CIPHER_param_to_asn1(EVP_CIPHER_CTX *c, ASN1_TYPE *type);
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int EVP_CIPHER_asn1_to_param(EVP_CIPHER_CTX *c, ASN1_TYPE *type);
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=head1 DESCRIPTION
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The EVP cipher routines are a high level interface to certain
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symmetric ciphers.
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EVP_EncryptInit() initialises a cipher context B<ctx> for encryption
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with cipher B<type>. B<type> is normally supplied by a function such
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as EVP_des_cbc() . B<key> is the symmetric key to use and B<iv> is the
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IV to use (if necessary), the actual number of bytes used for the
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key and IV depends on the cipher. It is possible to set all parameters
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to NULL except B<type> in an initial call and supply the remaining
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parameters in subsequent calls. This is normally done when the
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EVP_CIPHER_asn1_to_param() function is called to set the cipher
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parameters from an ASN1 AlgorithmIdentifier and the key from a
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different source.
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EVP_EncryptUpdate() encrypts B<inl> bytes from the buffer B<in> and
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writes the encrypted version to B<out>. This function can be called
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multiple times to encrypt successive blocks of data. The amount
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of data written depends on the block alignment of the encrypted data:
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as a result the amount of data written may be anything from zero bytes
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to (inl + cipher_block_size - 1) so B<outl> should contain sufficient
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room. The actual number of bytes written is placed in B<outl>.
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EVP_EncryptFinal() encrypts the "final" data, that is any data that
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remains in a partial block. It uses L<standard block padding|/NOTES> (aka PKCS
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padding). The encrypted final data is written to B<out> which should
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have sufficient space for one cipher block. The number of bytes written
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is placed in B<outl>. After this function is called the encryption operation
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is finished and no further calls to EVP_EncryptUpdate() should be made.
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EVP_DecryptInit(), EVP_DecryptUpdate() and EVP_DecryptFinal() are the
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corresponding decryption operations. EVP_DecryptFinal() will return an
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error code if the final block is not correctly formatted. The parameters
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and restrictions are identical to the encryption operations except that
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the decrypted data buffer B<out> passed to EVP_DecryptUpdate() should
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have sufficient room for (B<inl> + cipher_block_size) bytes unless the
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cipher block size is 1 in which case B<inl> bytes is sufficient.
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EVP_CipherInit(), EVP_CipherUpdate() and EVP_CipherFinal() are functions
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that can be used for decryption or encryption. The operation performed
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depends on the value of the B<enc> parameter. It should be set to 1 for
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encryption and 0 for decryption.
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EVP_CIPHER_CTX_cleanup() clears all information from a cipher context.
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It should be called after all operations using a cipher are complete
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so sensitive information does not remain in memory.
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EVP_get_cipherbyname(), EVP_get_cipherbynid() and EVP_get_cipherbyobj()
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return an EVP_CIPHER structure when passed a cipher name, a NID or an
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ASN1_OBJECT structure.
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EVP_CIPHER_nid() and EVP_CIPHER_CTX_nid() return the NID of a cipher when
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passed an B<EVP_CIPHER> or B<EVP_CIPHER_CTX> structure. The actual NID
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value is an internal value which may not have a corresponding OBJECT
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IDENTIFIER.
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EVP_CIPHER_key_length() and EVP_CIPHER_CTX_key_length() return the key
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length of a cipher when passed an B<EVP_CIPHER> or B<EVP_CIPHER_CTX>
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structure. The constant B<EVP_MAX_KEY_LENGTH> is the maximum key length
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for all ciphers.
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EVP_CIPHER_iv_length() and EVP_CIPHER_CTX_iv_length() return the IV
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length of a cipher when passed an B<EVP_CIPHER> or B<EVP_CIPHER_CTX>.
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It will return zero if the cipher does not use an IV. The constant
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B<EVP_MAX_IV_LENGTH> is the maximum IV length for all ciphers.
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EVP_CIPHER_block_size() and EVP_CIPHER_CTX_block_size() return the block
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size of a cipher when passed an B<EVP_CIPHER> or B<EVP_CIPHER_CTX>
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structure. The constant B<EVP_MAX_IV_LENGTH> is also the maximum block
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length for all ciphers.
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EVP_CIPHER_type() and EVP_CIPHER_CTX_type() return the type of the passed
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cipher or context. This "type" is the actual NID of the cipher OBJECT
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IDENTIFIER as such it ignores the cipher parameters and 40 bit RC2 and
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128 bit RC2 have the same NID. If the cipher does not have an object
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identifier or does not have ASN1 support this function will return
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B<NID_undef>.
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EVP_CIPHER_CTX_cipher() returns the B<EVP_CIPHER> structure when passed
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an B<EVP_CIPHER_CTX> structure.
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EVP_CIPHER_param_to_asn1() sets the AlgorithmIdentifier "parameter" based
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on the passed cipher. This will typically include any parameters and an
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IV. The cipher IV (if any) must be set when this call is made. This call
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should be made before the cipher is actually "used" (before any
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EVP_EncryptUpdate(), EVP_DecryptUpdate() calls for example). This function
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may fail if the cipher does not have any ASN1 support.
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EVP_CIPHER_asn1_to_param() sets the cipher parameters based on an ASN1
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AlgorithmIdentifier "parameter". The precise effect depends on the cipher
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In the case of RC2, for example, it will set the IV and effective key length.
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This function should be called after the base cipher type is set but before
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the key is set. For example EVP_CipherInit() will be called with the IV and
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key set to NULL, EVP_CIPHER_asn1_to_param() will be called and finally
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EVP_CipherInit() again with all parameters except the key set to NULL. It is
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possible for this function to fail if the cipher does not have any ASN1 support
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or the parameters cannot be set (for example the RC2 effective key length
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does not have an B<EVP_CIPHER> structure).
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=head1 RETURN VALUES
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EVP_EncryptInit(), EVP_EncryptUpdate() and EVP_EncryptFinal() do not return
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values.
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EVP_DecryptInit() and EVP_DecryptUpdate() do not return values.
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EVP_DecryptFinal() returns 0 if the decrypt failed or 1 for success.
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EVP_CipherInit() and EVP_CipherUpdate() do not return values.
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EVP_CipherFinal() returns 1 for a decryption failure or 1 for success, if
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the operation is encryption then it always returns 1.
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EVP_CIPHER_CTX_cleanup() does not return a value.
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EVP_get_cipherbyname(), EVP_get_cipherbynid() and EVP_get_cipherbyobj()
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return an B<EVP_CIPHER> structure or NULL on error.
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EVP_CIPHER_nid() and EVP_CIPHER_CTX_nid() return a NID.
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EVP_CIPHER_block_size() and EVP_CIPHER_CTX_block_size() return the block
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size.
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EVP_CIPHER_key_length() and EVP_CIPHER_CTX_key_length() return the key
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length.
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EVP_CIPHER_iv_length() and EVP_CIPHER_CTX_iv_length() return the IV
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length or zero if the cipher does not use an IV.
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EVP_CIPHER_type() and EVP_CIPHER_CTX_type() return the NID of the cipher's
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OBJECT IDENTIFIER or NID_undef if it has no defined OBJECT IDENTIFIER.
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EVP_CIPHER_CTX_cipher() returns an B<EVP_CIPHER> structure.
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EVP_CIPHER_param_to_asn1() and EVP_CIPHER_asn1_to_param() return 1 for
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success or zero for failure.
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=head1 NOTES
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Where possible the B<EVP> interface to symmetric ciphers should be used in
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preference to the low level interfaces. This is because the code then becomes
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transparent to the cipher used and much more flexible.
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PKCS padding works by adding B<n> padding bytes of value B<n> to make the total
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length of the encrypted data a multiple of the block size. Padding is always
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added so if the data is already a multiple of the block size B<n> will equal
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the block size. For example if the block size is 8 and 11 bytes are to be
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encrypted then 5 padding bytes of value 5 will be added.
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When decrypting the final block is checked to see if it has the correct form.
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Although the decryption operation can produce an error, it is not a strong
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test that the input data or key is correct. A random block has better than
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1 in 256 chance of being of the correct format and problems with the
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input data earlier on will not produce a final decrypt error.
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=head1 BUGS
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The current B<EVP> cipher interface is not as flexible as it should be. Only
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certain "spot" encryption algorithms can be used for ciphers which have various
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parameters associated with them (RC2, RC5 for example) this is inadequate.
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Several of the functions do not return error codes because the software versions
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can never fail. This is not true of hardware versions.
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=head1 SEE ALSO
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L<evp(3)|evp(3)>
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=head1 HISTORY
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=cut
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