EVP_EncodeInit.pod revision 298999 
1=pod
2
3=head1 NAME
4
5EVP_EncodeInit, EVP_EncodeUpdate, EVP_EncodeFinal, EVP_EncodeBlock,
6EVP_DecodeInit, EVP_DecodeUpdate, EVP_DecodeFinal, EVP_DecodeBlock - EVP base 64
7encode/decode routines
8
9=head1 SYNOPSIS
10
11 #include <openssl/evp.h>
12
13 void EVP_EncodeInit(EVP_ENCODE_CTX *ctx);
14 void EVP_EncodeUpdate(EVP_ENCODE_CTX *ctx, unsigned char *out, int *outl,
15                       const unsigned char *in, int inl);
16 void EVP_EncodeFinal(EVP_ENCODE_CTX *ctx, unsigned char *out, int *outl);
17 int EVP_EncodeBlock(unsigned char *t, const unsigned char *f, int n);
18
19 void EVP_DecodeInit(EVP_ENCODE_CTX *ctx);
20 int EVP_DecodeUpdate(EVP_ENCODE_CTX *ctx, unsigned char *out, int *outl,
21                      const unsigned char *in, int inl);
22 int EVP_DecodeFinal(EVP_ENCODE_CTX *ctx, unsigned
23                     char *out, int *outl);
24 int EVP_DecodeBlock(unsigned char *t, const unsigned char *f, int n);
25
26=head1 DESCRIPTION
27
28The EVP encode routines provide a high level interface to base 64 encoding and
29decoding. Base 64 encoding converts binary data into a printable form that uses
30the characters A-Z, a-z, 0-9, "+" and "/" to represent the data. For every 3
31bytes of binary data provided 4 bytes of base 64 encoded data will be produced
32plus some occasional newlines (see below). If the input data length is not a
33multiple of 3 then the output data will be padded at the end using the "="
34character.
35
36Encoding of binary data is performed in blocks of 48 input bytes (or less for
37the final block). For each 48 byte input block encoded 64 bytes of base 64 data
38is output plus an additional newline character (i.e. 65 bytes in total). The
39final block (which may be less than 48 bytes) will output 4 bytes for every 3
40bytes of input. If the data length is not divisible by 3 then a full 4 bytes is
41still output for the final 1 or 2 bytes of input. Similarly a newline character
42will also be output.
43
44EVP_EncodeInit() initialises B<ctx> for the start of a new encoding operation.
45
46EVP_EncodeUpdate() encode B<inl> bytes of data found in the buffer pointed to by
47B<in>. The output is stored in the buffer B<out> and the number of bytes output
48is stored in B<*outl>. It is the caller's responsibility to ensure that the
49buffer at B<out> is sufficiently large to accommodate the output data. Only full
50blocks of data (48 bytes) will be immediately processed and output by this
51function. Any remainder is held in the B<ctx> object and will be processed by a
52subsequent call to EVP_EncodeUpdate() or EVP_EncodeFinal(). To calculate the
53required size of the output buffer add together the value of B<inl> with the
54amount of unprocessed data held in B<ctx> and divide the result by 48 (ignore
55any remainder). This gives the number of blocks of data that will be processed.
56Ensure the output buffer contains 65 bytes of storage for each block, plus an
57additional byte for a NUL terminator. EVP_EncodeUpdate() may be called
58repeatedly to process large amounts of input data. In the event of an error
59EVP_EncodeUpdate() will set B<*outl> to 0.
60
61EVP_EncodeFinal() must be called at the end of an encoding operation. It will
62process any partial block of data remaining in the B<ctx> object. The output
63data will be stored in B<out> and the length of the data written will be stored
64in B<*outl>. It is the caller's responsibility to ensure that B<out> is
65sufficiently large to accommodate the output data which will never be more than
6665 bytes plus an additional NUL terminator (i.e. 66 bytes in total).
67
68EVP_EncodeBlock() encodes a full block of input data in B<f> and of length
69B<dlen> and stores it in B<t>. For every 3 bytes of input provided 4 bytes of
70output data will be produced. If B<dlen> is not divisible by 3 then the block is
71encoded as a final block of data and the output is padded such that it is always
72divisible by 4. Additionally a NUL terminator character will be added. For
73example if 16 bytes of input data is provided then 24 bytes of encoded data is
74created plus 1 byte for a NUL terminator (i.e. 25 bytes in total). The length of
75the data generated I<without> the NUL terminator is returned from the function.
76
77EVP_DecodeInit() initialises B<ctx> for the start of a new decoding operation.
78
79EVP_DecodeUpdate() decodes B<inl> characters of data found in the buffer pointed
80to by B<in>. The output is stored in the buffer B<out> and the number of bytes
81output is stored in B<*outl>. It is the caller's responsibility to ensure that
82the buffer at B<out> is sufficiently large to accommodate the output data. This
83function will attempt to decode as much data as possible in 4 byte chunks. Any
84whitespace, newline or carriage return characters are ignored. Any partial chunk
85of unprocessed data (1, 2 or 3 bytes) that remains at the end will be held in
86the B<ctx> object and processed by a subsequent call to EVP_DecodeUpdate(). If
87any illegal base 64 characters are encountered or if the base 64 padding
88character "=" is encountered in the middle of the data then the function returns
89-1 to indicate an error. A return value of 0 or 1 indicates successful
90processing of the data. A return value of 0 additionally indicates that the last
91input data characters processed included the base 64 padding character "=" and
92therefore no more non-padding character data is expected to be processed. For
93every 4 valid base 64 bytes processed (ignoring whitespace, carriage returns and
94line feeds), 3 bytes of binary output data will be produced (or less at the end
95of the data where the padding character "=" has been used).
96
97EVP_DecodeFinal() must be called at the end of a decoding operation. If there
98is any unprocessed data still in B<ctx> then the input data must not have been
99a multiple of 4 and therefore an error has occurred. The function will return -1
100in this case. Otherwise the function returns 1 on success.
101
102EVP_DecodeBlock() will decode the block of B<n> characters of base 64 data
103contained in B<f> and store the result in B<t>. Any leading whitespace will be
104trimmed as will any trailing whitespace, newlines, carriage returns or EOF
105characters. After such trimming the length of the data in B<f> must be divisbile
106by 4. For every 4 input bytes exactly 3 output bytes will be produced. The
107output will be padded with 0 bits if necessary to ensure that the output is
108always 3 bytes for every 4 input bytes. This function will return the length of
109the data decoded or -1 on error.
110
111=head1 RETURN VALUES
112
113EVP_EncodeBlock() returns the number of bytes encoded excluding the NUL
114terminator.
115
116EVP_DecodeUpdate() returns -1 on error and 0 or 1 on success. If 0 is returned
117then no more non-padding base 64 characters are expected.
118
119EVP_DecodeFinal() returns -1 on error or 1 on success.
120
121EVP_DecodeBlock() returns the length of the data decoded or -1 on error.
122
123=head1 SEE ALSO
124
125L<evp(3)>
126
127=cut
128