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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

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 dlen and stores it
       in t. For every 3 bytes of input provided 4 bytes of output data will be produced. If dlen
       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 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>.