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Command: EVP_EncodeInit | Section: 3 | Source: OpenBSD | File: EVP_EncodeInit.3
EVP_ENCODEINIT(3) FreeBSD 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
The EVP_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.
FreeBSD 14.1-RELEASE-p8 June 6, 2019 FreeBSD 14.1-RELEASE-p8