mirror of https://github.com/openssl/openssl.git
162 lines
8.0 KiB
Plaintext
162 lines
8.0 KiB
Plaintext
=pod
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=head1 NAME
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EVP_ENCODE_CTX_new, EVP_ENCODE_CTX_free, EVP_ENCODE_CTX_copy,
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EVP_ENCODE_CTX_num, EVP_EncodeInit, EVP_EncodeUpdate, EVP_EncodeFinal,
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EVP_EncodeBlock, EVP_DecodeInit, EVP_DecodeUpdate, EVP_DecodeFinal,
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EVP_DecodeBlock - EVP base 64 encode/decode routines
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=head1 SYNOPSIS
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#include <openssl/evp.h>
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EVP_ENCODE_CTX *EVP_ENCODE_CTX_new(void);
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void EVP_ENCODE_CTX_free(EVP_ENCODE_CTX *ctx);
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int EVP_ENCODE_CTX_copy(EVP_ENCODE_CTX *dctx, EVP_ENCODE_CTX *sctx);
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int EVP_ENCODE_CTX_num(EVP_ENCODE_CTX *ctx);
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void EVP_EncodeInit(EVP_ENCODE_CTX *ctx);
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int EVP_EncodeUpdate(EVP_ENCODE_CTX *ctx, unsigned char *out, int *outl,
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const unsigned char *in, int inl);
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void EVP_EncodeFinal(EVP_ENCODE_CTX *ctx, unsigned char *out, int *outl);
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int EVP_EncodeBlock(unsigned char *t, const unsigned char *f, int n);
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void EVP_DecodeInit(EVP_ENCODE_CTX *ctx);
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int EVP_DecodeUpdate(EVP_ENCODE_CTX *ctx, unsigned char *out, int *outl,
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const unsigned char *in, int inl);
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int EVP_DecodeFinal(EVP_ENCODE_CTX *ctx, unsigned char *out, int *outl);
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int EVP_DecodeBlock(unsigned char *t, const unsigned char *f, int n);
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=head1 DESCRIPTION
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The EVP encode routines provide a high level interface to base 64 encoding and
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decoding. Base 64 encoding converts binary data into a printable form that uses
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the characters A-Z, a-z, 0-9, "+" and "/" to represent the data. For every 3
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bytes of binary data provided 4 bytes of base 64 encoded data will be produced
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plus some occasional newlines (see below). If the input data length is not a
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multiple of 3 then the output data will be padded at the end using the "="
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character.
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EVP_ENCODE_CTX_new() allocates, initializes and returns a context to be used for
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the encode/decode functions.
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EVP_ENCODE_CTX_free() cleans up an encode/decode context B<ctx> and frees up the
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space allocated to it.
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Encoding of binary data is performed in blocks of 48 input bytes (or less for
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the final block). For each 48 byte input block encoded 64 bytes of base 64 data
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is output plus an additional newline character (i.e. 65 bytes in total). The
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final block (which may be less than 48 bytes) will output 4 bytes for every 3
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bytes of input. If the data length is not divisible by 3 then a full 4 bytes is
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still output for the final 1 or 2 bytes of input. Similarly a newline character
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will also be output.
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EVP_EncodeInit() initialises B<ctx> for the start of a new encoding operation.
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EVP_EncodeUpdate() encode B<inl> bytes of data found in the buffer pointed to by
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B<in>. The output is stored in the buffer B<out> and the number of bytes output
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is stored in B<*outl>. It is the caller's responsibility to ensure that the
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buffer at B<out> is sufficiently large to accommodate the output data. Only full
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blocks of data (48 bytes) will be immediately processed and output by this
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function. Any remainder is held in the B<ctx> object and will be processed by a
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subsequent call to EVP_EncodeUpdate() or EVP_EncodeFinal(). To calculate the
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required size of the output buffer add together the value of B<inl> with the
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amount of unprocessed data held in B<ctx> and divide the result by 48 (ignore
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any remainder). This gives the number of blocks of data that will be processed.
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Ensure the output buffer contains 65 bytes of storage for each block, plus an
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additional byte for a NUL terminator. EVP_EncodeUpdate() may be called
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repeatedly to process large amounts of input data. In the event of an error
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EVP_EncodeUpdate() will set B<*outl> to 0 and return 0. On success 1 will be
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returned.
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EVP_EncodeFinal() must be called at the end of an encoding operation. It will
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process any partial block of data remaining in the B<ctx> object. The output
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data will be stored in B<out> and the length of the data written will be stored
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in B<*outl>. It is the caller's responsibility to ensure that B<out> is
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sufficiently large to accommodate the output data which will never be more than
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65 bytes plus an additional NUL terminator (i.e. 66 bytes in total).
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EVP_ENCODE_CTX_copy() can be used to copy a context B<sctx> to a context
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B<dctx>. B<dctx> must be initialized before calling this function.
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EVP_ENCODE_CTX_num() will return the number of as yet unprocessed bytes still to
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be encoded or decoded that are pending in the B<ctx> object.
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EVP_EncodeBlock() encodes a full block of input data in B<f> and of length
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B<dlen> and stores it in B<t>. For every 3 bytes of input provided 4 bytes of
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output data will be produced. If B<dlen> is not divisible by 3 then the block is
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encoded as a final block of data and the output is padded such that it is always
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divisible by 4. Additionally a NUL terminator character will be added. For
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example if 16 bytes of input data is provided then 24 bytes of encoded data is
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created plus 1 byte for a NUL terminator (i.e. 25 bytes in total). The length of
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the data generated I<without> the NUL terminator is returned from the function.
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EVP_DecodeInit() initialises B<ctx> for the start of a new decoding operation.
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EVP_DecodeUpdate() decodes B<inl> characters of data found in the buffer pointed
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to by B<in>. The output is stored in the buffer B<out> and the number of bytes
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output is stored in B<*outl>. It is the caller's responsibility to ensure that
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the buffer at B<out> is sufficiently large to accommodate the output data. This
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function will attempt to decode as much data as possible in 4 byte chunks. Any
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whitespace, newline or carriage return characters are ignored. Any partial chunk
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of unprocessed data (1, 2 or 3 bytes) that remains at the end will be held in
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the B<ctx> object and processed by a subsequent call to EVP_DecodeUpdate(). If
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any illegal base 64 characters are encountered or if the base 64 padding
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character "=" is encountered in the middle of the data then the function returns
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-1 to indicate an error. A return value of 0 or 1 indicates successful
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processing of the data. A return value of 0 additionally indicates that the last
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input data characters processed included the base 64 padding character "=" and
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therefore no more non-padding character data is expected to be processed. For
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every 4 valid base 64 bytes processed (ignoring whitespace, carriage returns and
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line feeds), 3 bytes of binary output data will be produced (or less at the end
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of the data where the padding character "=" has been used).
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EVP_DecodeFinal() must be called at the end of a decoding operation. If there
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is any unprocessed data still in B<ctx> then the input data must not have been
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a multiple of 4 and therefore an error has occurred. The function will return -1
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in this case. Otherwise the function returns 1 on success.
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EVP_DecodeBlock() will decode the block of B<n> characters of base 64 data
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contained in B<f> and store the result in B<t>. Any leading whitespace will be
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trimmed as will any trailing whitespace, newlines, carriage returns or EOF
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characters. After such trimming the length of the data in B<f> must be divisible
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by 4. For every 4 input bytes exactly 3 output bytes will be produced. The
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output will be padded with 0 bits if necessary to ensure that the output is
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always 3 bytes for every 4 input bytes. This function will return the length of
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the data decoded or -1 on error.
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=head1 RETURN VALUES
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EVP_ENCODE_CTX_new() returns a pointer to the newly allocated EVP_ENCODE_CTX
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object or NULL on error.
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EVP_ENCODE_CTX_num() returns the number of bytes pending encoding or decoding in
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B<ctx>.
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EVP_EncodeUpdate() returns 0 on error or 1 on success.
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EVP_EncodeBlock() returns the number of bytes encoded excluding the NUL
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terminator.
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EVP_DecodeUpdate() returns -1 on error and 0 or 1 on success. If 0 is returned
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then no more non-padding base 64 characters are expected.
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EVP_DecodeFinal() returns -1 on error or 1 on success.
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EVP_DecodeBlock() returns the length of the data decoded or -1 on error.
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=head1 SEE ALSO
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L<evp(7)>
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=head1 COPYRIGHT
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Copyright 2016 The OpenSSL Project Authors. All Rights Reserved.
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Licensed under the Apache License 2.0 (the "License"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file LICENSE in the source distribution or at
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L<https://www.openssl.org/source/license.html>.
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=cut
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