NAME

       EVP_ENCODE_CTX_new, EVP_ENCODE_CTX_free, 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_num(EVP_ENCODE_CTX *ctx);
        void EVP_EncodeInit(EVP_ENCODE_CTX *ctx);
        void 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
       approximately 4 bytes of base 64 encoded data will be produced (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 base 64 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.

       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_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 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. 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 bytes 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 divisbile 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_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(3)