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135 .IX Title "EVP_EncodeInit 3"
136 .TH EVP_EncodeInit 3 "2016-09-22" "1.0.2i" "OpenSSL"
137 .\" For nroff, turn off justification. Always turn off hyphenation; it makes
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142 EVP_EncodeInit, EVP_EncodeUpdate, EVP_EncodeFinal, EVP_EncodeBlock,
143 EVP_DecodeInit, EVP_DecodeUpdate, EVP_DecodeFinal, EVP_DecodeBlock \- EVP base 64
144 encode/decode routines
146 .IX Header "SYNOPSIS"
148 \& #include <openssl/evp.h>
150 \& void EVP_EncodeInit(EVP_ENCODE_CTX *ctx);
151 \& void EVP_EncodeUpdate(EVP_ENCODE_CTX *ctx, unsigned char *out, int *outl,
152 \& const unsigned char *in, int inl);
153 \& void EVP_EncodeFinal(EVP_ENCODE_CTX *ctx, unsigned char *out, int *outl);
154 \& int EVP_EncodeBlock(unsigned char *t, const unsigned char *f, int n);
156 \& void EVP_DecodeInit(EVP_ENCODE_CTX *ctx);
157 \& int EVP_DecodeUpdate(EVP_ENCODE_CTX *ctx, unsigned char *out, int *outl,
158 \& const unsigned char *in, int inl);
159 \& int EVP_DecodeFinal(EVP_ENCODE_CTX *ctx, unsigned
160 \& char *out, int *outl);
161 \& int EVP_DecodeBlock(unsigned char *t, const unsigned char *f, int n);
164 .IX Header "DESCRIPTION"
165 The \s-1EVP\s0 encode routines provide a high level interface to base 64 encoding and
166 decoding. Base 64 encoding converts binary data into a printable form that uses
167 the characters A\-Z, a\-z, 0\-9, \*(L"+\*(R" and \*(L"/\*(R" to represent the data. For every 3
168 bytes of binary data provided 4 bytes of base 64 encoded data will be produced
169 plus some occasional newlines (see below). If the input data length is not a
170 multiple of 3 then the output data will be padded at the end using the \*(L"=\*(R"
173 Encoding of binary data is performed in blocks of 48 input bytes (or less for
174 the final block). For each 48 byte input block encoded 64 bytes of base 64 data
175 is output plus an additional newline character (i.e. 65 bytes in total). The
176 final block (which may be less than 48 bytes) will output 4 bytes for every 3
177 bytes of input. If the data length is not divisible by 3 then a full 4 bytes is
178 still output for the final 1 or 2 bytes of input. Similarly a newline character
181 \&\fIEVP_EncodeInit()\fR initialises \fBctx\fR for the start of a new encoding operation.
183 \&\fIEVP_EncodeUpdate()\fR encode \fBinl\fR bytes of data found in the buffer pointed to by
184 \&\fBin\fR. The output is stored in the buffer \fBout\fR and the number of bytes output
185 is stored in \fB*outl\fR. It is the caller's responsibility to ensure that the
186 buffer at \fBout\fR is sufficiently large to accommodate the output data. Only full
187 blocks of data (48 bytes) will be immediately processed and output by this
188 function. Any remainder is held in the \fBctx\fR object and will be processed by a
189 subsequent call to \fIEVP_EncodeUpdate()\fR or \fIEVP_EncodeFinal()\fR. To calculate the
190 required size of the output buffer add together the value of \fBinl\fR with the
191 amount of unprocessed data held in \fBctx\fR and divide the result by 48 (ignore
192 any remainder). This gives the number of blocks of data that will be processed.
193 Ensure the output buffer contains 65 bytes of storage for each block, plus an
194 additional byte for a \s-1NUL\s0 terminator. \fIEVP_EncodeUpdate()\fR may be called
195 repeatedly to process large amounts of input data. In the event of an error
196 \&\fIEVP_EncodeUpdate()\fR will set \fB*outl\fR to 0.
198 \&\fIEVP_EncodeFinal()\fR must be called at the end of an encoding operation. It will
199 process any partial block of data remaining in the \fBctx\fR object. The output
200 data will be stored in \fBout\fR and the length of the data written will be stored
201 in \fB*outl\fR. It is the caller's responsibility to ensure that \fBout\fR is
202 sufficiently large to accommodate the output data which will never be more than
203 65 bytes plus an additional \s-1NUL\s0 terminator (i.e. 66 bytes in total).
205 \&\fIEVP_EncodeBlock()\fR encodes a full block of input data in \fBf\fR and of length
206 \&\fBdlen\fR and stores it in \fBt\fR. For every 3 bytes of input provided 4 bytes of
207 output data will be produced. If \fBdlen\fR is not divisible by 3 then the block is
208 encoded as a final block of data and the output is padded such that it is always
209 divisible by 4. Additionally a \s-1NUL\s0 terminator character will be added. For
210 example if 16 bytes of input data is provided then 24 bytes of encoded data is
211 created plus 1 byte for a \s-1NUL\s0 terminator (i.e. 25 bytes in total). The length of
212 the data generated \fIwithout\fR the \s-1NUL\s0 terminator is returned from the function.
214 \&\fIEVP_DecodeInit()\fR initialises \fBctx\fR for the start of a new decoding operation.
216 \&\fIEVP_DecodeUpdate()\fR decodes \fBinl\fR characters of data found in the buffer pointed
217 to by \fBin\fR. The output is stored in the buffer \fBout\fR and the number of bytes
218 output is stored in \fB*outl\fR. It is the caller's responsibility to ensure that
219 the buffer at \fBout\fR is sufficiently large to accommodate the output data. This
220 function will attempt to decode as much data as possible in 4 byte chunks. Any
221 whitespace, newline or carriage return characters are ignored. Any partial chunk
222 of unprocessed data (1, 2 or 3 bytes) that remains at the end will be held in
223 the \fBctx\fR object and processed by a subsequent call to \fIEVP_DecodeUpdate()\fR. If
224 any illegal base 64 characters are encountered or if the base 64 padding
225 character \*(L"=\*(R" is encountered in the middle of the data then the function returns
226 \&\-1 to indicate an error. A return value of 0 or 1 indicates successful
227 processing of the data. A return value of 0 additionally indicates that the last
228 input data characters processed included the base 64 padding character \*(L"=\*(R" and
229 therefore no more non-padding character data is expected to be processed. For
230 every 4 valid base 64 bytes processed (ignoring whitespace, carriage returns and
231 line feeds), 3 bytes of binary output data will be produced (or less at the end
232 of the data where the padding character \*(L"=\*(R" has been used).
234 \&\fIEVP_DecodeFinal()\fR must be called at the end of a decoding operation. If there
235 is any unprocessed data still in \fBctx\fR then the input data must not have been
236 a multiple of 4 and therefore an error has occurred. The function will return \-1
237 in this case. Otherwise the function returns 1 on success.
239 \&\fIEVP_DecodeBlock()\fR will decode the block of \fBn\fR characters of base 64 data
240 contained in \fBf\fR and store the result in \fBt\fR. Any leading whitespace will be
241 trimmed as will any trailing whitespace, newlines, carriage returns or \s-1EOF\s0
242 characters. After such trimming the length of the data in \fBf\fR must be divisbile
243 by 4. For every 4 input bytes exactly 3 output bytes will be produced. The
244 output will be padded with 0 bits if necessary to ensure that the output is
245 always 3 bytes for every 4 input bytes. This function will return the length of
246 the data decoded or \-1 on error.
248 .IX Header "RETURN VALUES"
249 \&\fIEVP_EncodeBlock()\fR returns the number of bytes encoded excluding the \s-1NUL\s0
252 \&\fIEVP_DecodeUpdate()\fR returns \-1 on error and 0 or 1 on success. If 0 is returned
253 then no more non-padding base 64 characters are expected.
255 \&\fIEVP_DecodeFinal()\fR returns \-1 on error or 1 on success.
257 \&\fIEVP_DecodeBlock()\fR returns the length of the data decoded or \-1 on error.
259 .IX Header "SEE ALSO"