EVP_ENCODEINIT(3SSL) OpenSSL EVP_ENCODEINIT(3SSL)
NAME
EVP_ENCODE_CTX_new, EVP_ENCODE_CTX_free, EVP_ENCODE_CTX_copy,
EVP_ENCODE_CTX_num, 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);
int EVP_ENCODE_CTX_copy(EVP_ENCODE_CTX *dctx, EVP_ENCODE_CTX *sctx);
int EVP_ENCODE_CTX_num(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 (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.
EVP_ENCODE_CTX_new() allocates, initializes and returns a context to be
used for the encode/decode functions.
EVP_ENCODE_CTX_free() cleans up an encode/decode context ctx and frees
up the space allocated to it. If the argument is NULL, nothing is done.
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() 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 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_ENCODE_CTX_copy() can be used to copy a context sctx to a context
dctx. dctx must be initialized before calling this function.
EVP_ENCODE_CTX_num() will return the number of as yet unprocessed bytes
still to be encoded or decoded that are pending in the ctx object.
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 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 chunks of up to 80 base64 characters at a time. Residual
input shorter than the internal chunk size will be buffered in ctx if
its length is not a multiple of 4 (including any padding), to be
processed in future calls to EVP_DecodeUpdate() or EVP_DecodeFinal().
If the final chunk length is a multiple of 4, it is decoded immediately
and not buffered.
Any whitespace, newline or carriage return characters are ignored. For
compatibility with PEM, the - (hyphen) character is treated as a soft
end-of-input, subsequent bytes are not buffered, and the return value
will be 0 to indicate that the end of the base64 input has been
detected. The soft end-of-input, if present, MUST occur after a
multiple of 4 valid base64 input bytes. The soft end-of-input condition
is not remembered in ctx, it is up to the caller to avoid further calls
to EVP_DecodeUpdate() after a 0 or negative (error) return.
If any invalid base64 characters are encountered or if the base64
padding character (=) is encountered in the middle of the data then
EVP_DecodeUpdate() 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 4 bytes processed ended with base64
padding (=), or that the next 4 byte group starts with the soft end-of-
input (-) character, and therefore no more input 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
(except at the end of data terminated with one or two padding
characters).
EVP_DecodeFinal() should be called at the end of a decoding operation,
but it will never decode additional data. If there is no residual data
it will return 1 to indicate success. If there is residual data, its
length is not a multiple of 4, i.e. it was not properly padded, -1 is is
returned in that case to indicate an error.
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. Internal whitespace MUST NOT be present. After
trimming the data in f MUST consist entirely of valid base64 characters
or padding (only at the tail of the input) and its length MUST be
divisible by 4. For every 4 input bytes exactly 3 output bytes will be
produced. Padding bytes (=) (even if internal) are decoded to 6 zero
bits, the caller is responsible for taking trailing padding into
account, by ignoring as many bytes at the tail of the returned output.
EVP_DecodeBlock() 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_ENCODE_CTX_num() returns the number of bytes pending encoding or
decoding in ctx.
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
evp(7)
HISTORY
The EVP_DecodeUpdate() function was fixed in OpenSSL 3.5, so now it
produces the number of bytes specified in outl* and does not decode
padding bytes (=) to 6 zero bits.
COPYRIGHT
Copyright 2016-2025 The OpenSSL Project Authors. All Rights Reserved.
Licensed under the Apache License 2.0 (the "License"). You may not use
this file except in compliance with the License. You can obtain a copy
in the file LICENSE in the source distribution or at
<https://www.openssl.org/source/license.html>.
3.5.7 2026-06-09 EVP_ENCODEINIT(3SSL)
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