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
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.