1EVP_EncodeInit(3)                   OpenSSL                  EVP_EncodeInit(3)
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NAME

6       EVP_EncodeInit, EVP_EncodeUpdate, EVP_EncodeFinal, EVP_EncodeBlock,
7       EVP_DecodeInit, EVP_DecodeUpdate, EVP_DecodeFinal, EVP_DecodeBlock -
8       EVP base 64 encode/decode routines
9

SYNOPSIS

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

DESCRIPTION

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

120       EVP_EncodeBlock() returns the number of bytes encoded excluding the NUL
121       terminator.
122
123       EVP_DecodeUpdate() returns -1 on error and 0 or 1 on success. If 0 is
124       returned then no more non-padding base 64 characters are expected.
125
126       EVP_DecodeFinal() returns -1 on error or 1 on success.
127
128       EVP_DecodeBlock() returns the length of the data decoded or -1 on
129       error.
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SEE ALSO

132       evp(3)
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1361.0.2o                            2019-09-10                 EVP_EncodeInit(3)
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