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 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 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)