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135 .\" ========================================================================
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137 .IX Title "EVP_SealInit 3"
138 .TH EVP_SealInit 3 "2009-07-19" "1.0.1n" "OpenSSL"
139 .\" For nroff, turn off justification. Always turn off hyphenation; it makes
140 .\" way too many mistakes in technical documents.
141 .if n .ad l
142 .nh
143 .SH "NAME"
144 EVP_SealInit, EVP_SealUpdate, EVP_SealFinal \- EVP envelope encryption
145 .SH "LIBRARY"
146 libcrypto, -lcrypto
147 .SH "SYNOPSIS"
148 .IX Header "SYNOPSIS"
149 .Vb 1
150 \& #include <openssl/evp.h>
151 \&
152 \& int EVP_SealInit(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type,
153 \& unsigned char **ek, int *ekl, unsigned char *iv,
154 \& EVP_PKEY **pubk, int npubk);
155 \& int EVP_SealUpdate(EVP_CIPHER_CTX *ctx, unsigned char *out,
156 \& int *outl, unsigned char *in, int inl);
157 \& int EVP_SealFinal(EVP_CIPHER_CTX *ctx, unsigned char *out,
158 \& int *outl);
159 .Ve
160 .SH "DESCRIPTION"
161 .IX Header "DESCRIPTION"
162 The \s-1EVP\s0 envelope routines are a high level interface to envelope
163 encryption. They generate a random key and \s-1IV \s0(if required) then
164 \&\*(L"envelope\*(R" it by using public key encryption. Data can then be
165 encrypted using this key.
166 .PP
167 \&\fIEVP_SealInit()\fR initializes a cipher context \fBctx\fR for encryption
168 with cipher \fBtype\fR using a random secret key and \s-1IV. \s0\fBtype\fR is normally
169 supplied by a function such as \fIEVP_des_cbc()\fR. The secret key is encrypted
170 using one or more public keys, this allows the same encrypted data to be
171 decrypted using any of the corresponding private keys. \fBek\fR is an array of
172 buffers where the public key encrypted secret key will be written, each buffer
173 must contain enough room for the corresponding encrypted key: that is
174 \&\fBek[i]\fR must have room for \fBEVP_PKEY_size(pubk[i])\fR bytes. The actual
175 size of each encrypted secret key is written to the array \fBekl\fR. \fBpubk\fR is
176 an array of \fBnpubk\fR public keys.
177 .PP
178 The \fBiv\fR parameter is a buffer where the generated \s-1IV\s0 is written to. It must
179 contain enough room for the corresponding cipher's \s-1IV,\s0 as determined by (for
180 example) EVP_CIPHER_iv_length(type).
181 .PP
182 If the cipher does not require an \s-1IV\s0 then the \fBiv\fR parameter is ignored
183 and can be \fB\s-1NULL\s0\fR.
184 .PP
185 \&\fIEVP_SealUpdate()\fR and \fIEVP_SealFinal()\fR have exactly the same properties
186 as the \fIEVP_EncryptUpdate()\fR and \fIEVP_EncryptFinal()\fR routines, as
187 documented on the \fIEVP_EncryptInit\fR\|(3) manual
188 page.
189 .SH "RETURN VALUES"
190 .IX Header "RETURN VALUES"
191 \&\fIEVP_SealInit()\fR returns 0 on error or \fBnpubk\fR if successful.
192 .PP
193 \&\fIEVP_SealUpdate()\fR and \fIEVP_SealFinal()\fR return 1 for success and 0 for
194 failure.
195 .SH "NOTES"
196 .IX Header "NOTES"
197 Because a random secret key is generated the random number generator
198 must be seeded before calling \fIEVP_SealInit()\fR.
199 .PP
200 The public key must be \s-1RSA\s0 because it is the only OpenSSL public key
201 algorithm that supports key transport.
202 .PP
203 Envelope encryption is the usual method of using public key encryption
204 on large amounts of data, this is because public key encryption is slow
205 but symmetric encryption is fast. So symmetric encryption is used for
206 bulk encryption and the small random symmetric key used is transferred
207 using public key encryption.
208 .PP
209 It is possible to call \fIEVP_SealInit()\fR twice in the same way as
210 \&\fIEVP_EncryptInit()\fR. The first call should have \fBnpubk\fR set to 0
211 and (after setting any cipher parameters) it should be called again
212 with \fBtype\fR set to \s-1NULL.\s0
213 .SH "SEE ALSO"
214 .IX Header "SEE ALSO"
215 \&\fIopenssl_evp\fR\|(3), \fIopenssl_rand\fR\|(3),
216 \&\fIEVP_EncryptInit\fR\|(3),
217 \&\fIEVP_OpenInit\fR\|(3)
218 .SH "HISTORY"
219 .IX Header "HISTORY"
220 \&\fIEVP_SealFinal()\fR did not return a value before OpenSSL 0.9.7.