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136 .IX Title "EVP_SealInit 3"
137 .TH EVP_SealInit 3 "2005-03-29" "1.1.0-dev" "OpenSSL"
138 .\" For nroff, turn off justification. Always turn off hyphenation; it makes
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140 .if n .ad l
141 .nh
142 .SH "NAME"
143 EVP_SealInit, EVP_SealUpdate, EVP_SealFinal \- EVP envelope encryption
144 .SH "LIBRARY"
145 libcrypto, -lcrypto
146 .SH "SYNOPSIS"
147 .IX Header "SYNOPSIS"
148 .Vb 1
149 \& #include <openssl/evp.h>
150 \&
151 \& int EVP_SealInit(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type,
152 \& unsigned char **ek, int *ekl, unsigned char *iv,
153 \& EVP_PKEY **pubk, int npubk);
154 \& int EVP_SealUpdate(EVP_CIPHER_CTX *ctx, unsigned char *out,
155 \& int *outl, unsigned char *in, int inl);
156 \& int EVP_SealFinal(EVP_CIPHER_CTX *ctx, unsigned char *out,
157 \& int *outl);
158 .Ve
159 .SH "DESCRIPTION"
160 .IX Header "DESCRIPTION"
161 The \s-1EVP\s0 envelope routines are a high level interface to envelope
162 encryption. They generate a random key and \s-1IV\s0 (if required) then
163 \&\*(L"envelope\*(R" it by using public key encryption. Data can then be
164 encrypted using this key.
165 .PP
166 \&\fIEVP_SealInit()\fR initializes a cipher context \fBctx\fR for encryption
167 with cipher \fBtype\fR using a random secret key and \s-1IV\s0. \fBtype\fR is normally
168 supplied by a function such as \fIEVP_des_cbc()\fR. The secret key is encrypted
169 using one or more public keys, this allows the same encrypted data to be
170 decrypted using any of the corresponding private keys. \fBek\fR is an array of
171 buffers where the public key encrypted secret key will be written, each buffer
172 must contain enough room for the corresponding encrypted key: that is
173 \&\fBek[i]\fR must have room for \fBEVP_PKEY_size(pubk[i])\fR bytes. The actual
174 size of each encrypted secret key is written to the array \fBekl\fR. \fBpubk\fR is
175 an array of \fBnpubk\fR public keys.
176 .PP
177 The \fBiv\fR parameter is a buffer where the generated \s-1IV\s0 is written to. It must
178 contain enough room for the corresponding cipher's \s-1IV\s0, as determined by (for
179 example) EVP_CIPHER_iv_length(type).
180 .PP
181 If the cipher does not require an \s-1IV\s0 then the \fBiv\fR parameter is ignored
182 and can be \fB\s-1NULL\s0\fR.
183 .PP
184 \&\fIEVP_SealUpdate()\fR and \fIEVP_SealFinal()\fR have exactly the same properties
185 as the \fIEVP_EncryptUpdate()\fR and \fIEVP_EncryptFinal()\fR routines, as
186 documented on the \fIEVP_EncryptInit\fR\|(3) manual
187 page.
188 .SH "RETURN VALUES"
189 .IX Header "RETURN VALUES"
190 \&\fIEVP_SealInit()\fR returns 0 on error or \fBnpubk\fR if successful.
191 .PP
192 \&\fIEVP_SealUpdate()\fR and \fIEVP_SealFinal()\fR return 1 for success and 0 for
193 failure.
194 .SH "NOTES"
195 .IX Header "NOTES"
196 Because a random secret key is generated the random number generator
197 must be seeded before calling \fIEVP_SealInit()\fR.
198 .PP
199 The public key must be \s-1RSA\s0 because it is the only OpenSSL public key
200 algorithm that supports key transport.
201 .PP
202 Envelope encryption is the usual method of using public key encryption
203 on large amounts of data, this is because public key encryption is slow
204 but symmetric encryption is fast. So symmetric encryption is used for
205 bulk encryption and the small random symmetric key used is transferred
206 using public key encryption.
207 .PP
208 It is possible to call \fIEVP_SealInit()\fR twice in the same way as
209 \&\fIEVP_EncryptInit()\fR. The first call should have \fBnpubk\fR set to 0
210 and (after setting any cipher parameters) it should be called again
211 with \fBtype\fR set to \s-1NULL\s0.
212 .SH "SEE ALSO"
213 .IX Header "SEE ALSO"
214 \&\fIopenssl_evp\fR\|(3), \fIopenssl_rand\fR\|(3),
215 \&\fIEVP_EncryptInit\fR\|(3),
216 \&\fIEVP_OpenInit\fR\|(3)
217 .SH "HISTORY"
218 .IX Header "HISTORY"
219 \&\fIEVP_SealFinal()\fR did not return a value before OpenSSL 0.9.7.