Updated: 2021/Apr/14


EVP_EncodeInit(3)                   OpenSSL                  EVP_EncodeInit(3)



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 base 64 encode/decode routines

LIBRARY
       libcrypto, -lcrypto

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 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.

       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.

       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 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 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 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_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 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(7)

COPYRIGHT
       Copyright 2016-2020 The OpenSSL Project Authors. All Rights Reserved.

       Licensed under the OpenSSL license (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>.



1.1.1i                            2020-12-10                 EVP_EncodeInit(3)