EVP_EncodeInit(3) OpenSSL EVP_EncodeInit(3)
NAME
EVP_ENCODE_CTX_new, EVP_ENCODE_CTX_free, EVP_ENCODE_CTX_copy,
EVP_ENCODE_CTX_num, EVP_EncodeInit, EVP_EncodeUpdate, EVP_EncodeFinal,
EVP_EncodeBlock, EVP_DecodeInit, EVP_DecodeUpdate, EVP_DecodeFinal,
EVP_DecodeBlock - EVP base 64 encode/decode routines
SYNOPSIS
#include <openssl/evp.h>
EVP_ENCODE_CTX *EVP_ENCODE_CTX_new(void);
void EVP_ENCODE_CTX_free(EVP_ENCODE_CTX *ctx);
int EVP_ENCODE_CTX_copy(EVP_ENCODE_CTX *dctx, EVP_ENCODE_CTX *sctx);
int EVP_ENCODE_CTX_num(EVP_ENCODE_CTX *ctx);
void EVP_EncodeInit(EVP_ENCODE_CTX *ctx);
int EVP_EncodeUpdate(EVP_ENCODE_CTX *ctx, unsigned char *out, int *outl,
const unsigned char *in, int inl);
void EVP_EncodeFinal(EVP_ENCODE_CTX *ctx, unsigned char *out, int *outl);
int EVP_EncodeBlock(unsigned char *t, const unsigned char *f, int n);
void EVP_DecodeInit(EVP_ENCODE_CTX *ctx);
int EVP_DecodeUpdate(EVP_ENCODE_CTX *ctx, unsigned char *out, int *outl,
const unsigned char *in, int inl);
int EVP_DecodeFinal(EVP_ENCODE_CTX *ctx, unsigned char *out, int *outl);
int EVP_DecodeBlock(unsigned char *t, const unsigned char *f, int n);
DESCRIPTION
The EVP encode routines provide a high-level interface to base 64
encoding and decoding. Base 64 encoding converts binary data into a
printable form that uses the characters A-Z, a-z, 0-9, "+" and "/" to
represent the data. For every 3 bytes of binary data provided 4 bytes
of base 64 encoded data will be produced plus some occasional newlines
(see below). If the input data length is not a multiple of 3 then the
output data will be padded at the end using the "=" character.
EVP_ENCODE_CTX_new() allocates, initializes and returns a context to be
used for the encode/decode functions.
EVP_ENCODE_CTX_free() cleans up an encode/decode context ctx and frees
up the space allocated to it.
Encoding of binary data is performed in blocks of 48 input bytes (or
less for the final block). For each 48 byte input block encoded 64
bytes of base 64 data is output plus an additional newline character
(i.e. 65 bytes in total). The final block (which may be less than 48
bytes) will output 4 bytes for every 3 bytes of input. If the data
length is not divisible by 3 then a full 4 bytes is still output for
the final 1 or 2 bytes of input. Similarly a newline character will
also be output.
EVP_EncodeInit() initialises ctx for the start of a new encoding
operation.
EVP_EncodeUpdate() encode inl bytes of data found in the buffer pointed
to by in. The output is stored in the buffer out and the number of
bytes output is stored in *outl. It is the caller's responsibility to
ensure that the buffer at out is sufficiently large to accommodate the
output data. Only full blocks of data (48 bytes) will be immediately
processed and output by this function. Any remainder is held in the ctx
object and will be processed by a subsequent call to EVP_EncodeUpdate()
or EVP_EncodeFinal(). To calculate the required size of the output
buffer add together the value of inl with the amount of unprocessed
data held in ctx and divide the result by 48 (ignore any remainder).
This gives the number of blocks of data that will be processed. Ensure
the output buffer contains 65 bytes of storage for each block, plus an
additional byte for a NUL terminator. EVP_EncodeUpdate() may be called
repeatedly to process large amounts of input data. In the event of an
error EVP_EncodeUpdate() will set *outl to 0 and return 0. On success 1
will be returned.
EVP_EncodeFinal() must be called at the end of an encoding operation.
It will process any partial block of data remaining in the ctx object.
The output data will be stored in out and the length of the data
written will be stored in *outl. It is the caller's responsibility to
ensure that out is sufficiently large to accommodate the output data
which will never be more than 65 bytes plus an additional NUL
terminator (i.e. 66 bytes in total).
EVP_ENCODE_CTX_copy() can be used to copy a context sctx to a context
dctx. dctx must be initialized before calling this function.
EVP_ENCODE_CTX_num() will return the number of as yet unprocessed bytes
still to be encoded or decoded that are pending in the ctx object.
EVP_EncodeBlock() encodes a full block of input data in f and of length
n and stores it in t. For every 3 bytes of input provided 4 bytes of
output data will be produced. If n is not divisible by 3 then the block
is encoded as a final block of data and the output is padded such that
it is always divisible by 4. Additionally a NUL terminator character
will be added. For example if 16 bytes of input data is provided then
24 bytes of encoded data is created plus 1 byte for a NUL terminator
(i.e. 25 bytes in total). The length of the data generated without the
NUL terminator is returned from the function.
EVP_DecodeInit() initialises ctx for the start of a new decoding
operation.
EVP_DecodeUpdate() decodes inl characters of data found in the buffer
pointed to by in. The output is stored in the buffer out and the number
of bytes output is stored in *outl. It is the caller's responsibility
to ensure that the buffer at out is sufficiently large to accommodate
the output data. This function will attempt to decode as much data as
possible in 4 byte chunks. Any whitespace, newline or carriage return
characters are ignored. Any partial chunk of unprocessed data (1, 2 or
3 bytes) that remains at the end will be held in the ctx object and
processed by a subsequent call to EVP_DecodeUpdate(). If any illegal
base 64 characters are encountered or if the base 64 padding character
"=" is encountered in the middle of the data then the function returns
-1 to indicate an error. A return value of 0 or 1 indicates successful
processing of the data. A return value of 0 additionally indicates that
the last input data characters processed included the base 64 padding
character "=" and therefore no more non-padding character data is
expected to be processed. For every 4 valid base 64 bytes processed
(ignoring whitespace, carriage returns and line feeds), 3 bytes of
binary output data will be produced (or less at the end of the data
where the padding character "=" has been used).
EVP_DecodeFinal() must be called at the end of a decoding operation. If
there is any unprocessed data still in ctx then the input data must not
have been a multiple of 4 and therefore an error has occurred. The
function will return -1 in this case. Otherwise the function returns 1
on success.
EVP_DecodeBlock() will decode the block of n characters of base 64 data
contained in f and store the result in t. Any leading whitespace will
be trimmed as will any trailing whitespace, newlines, carriage returns
or EOF characters. After such trimming the length of the data in f must
be divisible by 4. For every 4 input bytes exactly 3 output bytes will
be produced. The output will be padded with 0 bits if necessary to
ensure that the output is always 3 bytes for every 4 input bytes. This
function will return the length of the data decoded or -1 on error.
RETURN VALUES
EVP_ENCODE_CTX_new() returns a pointer to the newly allocated
EVP_ENCODE_CTX object or NULL on error.
EVP_ENCODE_CTX_num() returns the number of bytes pending encoding or
decoding in ctx.
EVP_EncodeUpdate() returns 0 on error or 1 on success.
EVP_EncodeBlock() returns the number of bytes encoded excluding the NUL
terminator.
EVP_DecodeUpdate() returns -1 on error and 0 or 1 on success. If 0 is
returned then no more non-padding base 64 characters are expected.
EVP_DecodeFinal() returns -1 on error or 1 on success.
EVP_DecodeBlock() returns the length of the data decoded or -1 on
error.
SEE ALSO
evp(7)
COPYRIGHT
Copyright 2016-2020 The OpenSSL Project Authors. All Rights Reserved.
Licensed under the OpenSSL license (the "License"). You may not use
this file except in compliance with the License. You can obtain a copy
in the file LICENSE in the source distribution or at
<https://www.openssl.org/source/license.html>.
1.1.1h 2020-09-22 EVP_EncodeInit(3)
openssl 1.1.1h - Generated Sat Oct 3 08:12:04 CDT 2020