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EVP_ENCODEINIT(3) | Library Functions Manual | EVP_ENCODEINIT(3) |
NAME
EVP_ENCODE_CTX_new
,
EVP_ENCODE_CTX_free
,
EVP_EncodeInit
,
EVP_EncodeUpdate
,
EVP_EncodeFinal
,
EVP_EncodeBlock
,
EVP_DecodeInit
,
EVP_DecodeUpdate
,
EVP_DecodeFinal
,
EVP_DecodeBlock
—
EVP base64 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);
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 base64 encoding and decoding. Base64 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 base64-encoded data will be produced, plus some occasional newlines. 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 and decode functions.
EVP_ENCODE_CTX_free
() frees
ctx.
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 base64
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
() encodes
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_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 are
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 base64
characters are encountered or if the base64 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 base64 padding character "=" and
therefore no more non-padding character data is expected to be processed. For
every 4 valid base64 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 base64 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_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 base64 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
BIO_f_base64(3), evp(3)HISTORY
TheEVP_Encode*
() and
EVP_Decode*
() functions first appeared in
SSLeay 0.5.1 and have been available since OpenBSD
2.4.
EVP_ENCODE_CTX_new
() and
EVP_ENCODE_CTX_free
() first appeared in
OpenSSL 1.1.0 and have been available since OpenBSD
6.5.June 6, 2019 | Debian |