/usr/man/cat.3/EVP_EncodeInit.3
EVP_EncodeInit(3) OpenSSL EVP_EncodeInit(3)
NAME
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>
void EVP_EncodeInit(EVP_ENCODE_CTX *ctx);
void 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.
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
1.0.2t Last change: 2019-09-10 1
EVP_EncodeInit(3) OpenSSL EVP_EncodeInit(3)
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.
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_EncodeBlock() encodes a full block of input data in f
and of length dlen and stores it in t. For every 3 bytes of
input provided 4 bytes of output data will be produced. If
dlen 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
1.0.2t Last change: 2019-09-10 2
EVP_EncodeInit(3) OpenSSL EVP_EncodeInit(3)
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
divisbile 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_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(3)
1.0.2t Last change: 2019-09-10 3
See also EVP_DecodeBlock(3)
See also EVP_DecodeFinal(3)
See also EVP_DecodeInit(3)
See also EVP_DecodeUpdate(3)
See also EVP_EncodeBlock(3)
See also EVP_EncodeFinal(3)
See also EVP_EncodeUpdate(3)
Man(1) output converted with
man2html