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+=pod
+
+=head1 NAME
+
+EVP_EncodeInit, EVP_EncodeUpdate, EVP_EncodeFinal, EVP_EncodeBlock,
+EVP_DecodeInit, EVP_DecodeUpdate, EVP_DecodeFinal, EVP_DecodeBlock - EVP base 64
+encode/decode routines
+
+=head1 SYNOPSIS
+
+ #include <openssl/evp.h>
+
+ 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);
+
+=head1 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.
+
+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 B<ctx> for the start of a new encoding operation.
+
+EVP_EncodeUpdate() encode B<inl> bytes of data found in the buffer pointed to by
+B<in>. The output is stored in the buffer B<out> and the number of bytes output
+is stored in B<*outl>. It is the caller's responsibility to ensure that the
+buffer at B<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 B<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 B<inl> with the
+amount of unprocessed data held in B<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 B<*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 B<ctx> object. The output
+data will be stored in B<out> and the length of the data written will be stored
+in B<*outl>. It is the caller's responsibility to ensure that B<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 B<f> and of length
+B<dlen> and stores it in B<t>. For every 3 bytes of input provided 4 bytes of
+output data will be produced. If B<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 I<without> the NUL terminator is returned from the function.
+
+EVP_DecodeInit() initialises B<ctx> for the start of a new decoding operation.
+
+EVP_DecodeUpdate() decodes B<inl> characters of data found in the buffer pointed
+to by B<in>. The output is stored in the buffer B<out> and the number of bytes
+output is stored in B<*outl>. It is the caller's responsibility to ensure that
+the buffer at B<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 B<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 B<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 B<n> characters of base 64 data
+contained in B<f> and store the result in B<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 B<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.
+
+=head1 RETURN VALUES
+
+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.
+
+=head1 SEE ALSO
+
+L<evp(3)>
+
+=cut