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124 .\" ========================================================================
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126 .IX Title "EVP_SealInit 3"
127 .TH EVP_SealInit 3 "2007-10-24" "0.9.8g" "OpenSSL"
128 .\" For nroff, turn off justification. Always turn off hyphenation; it makes
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130 .if n .ad l
131 .nh
132 .SH "NAME"
133 EVP_SealInit, EVP_SealUpdate, EVP_SealFinal \- EVP envelope encryption
134 .SH "SYNOPSIS"
135 .IX Header "SYNOPSIS"
136 .Vb 1
137 \& #include <openssl/evp.h>
138 \&
139 \& int EVP_SealInit(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type,
140 \& unsigned char **ek, int *ekl, unsigned char *iv,
141 \& EVP_PKEY **pubk, int npubk);
142 \& int EVP_SealUpdate(EVP_CIPHER_CTX *ctx, unsigned char *out,
143 \& int *outl, unsigned char *in, int inl);
144 \& int EVP_SealFinal(EVP_CIPHER_CTX *ctx, unsigned char *out,
145 \& int *outl);
146 .Ve
147 .SH "DESCRIPTION"
148 .IX Header "DESCRIPTION"
149 The \s-1EVP\s0 envelope routines are a high level interface to envelope
150 encryption. They generate a random key and \s-1IV\s0 (if required) then
151 \&\*(L"envelope\*(R" it by using public key encryption. Data can then be
152 encrypted using this key.
153 .PP
154 \&\fIEVP_SealInit()\fR initializes a cipher context \fBctx\fR for encryption
155 with cipher \fBtype\fR using a random secret key and \s-1IV\s0. \fBtype\fR is normally
156 supplied by a function such as \fIEVP_des_cbc()\fR. The secret key is encrypted
157 using one or more public keys, this allows the same encrypted data to be
158 decrypted using any of the corresponding private keys. \fBek\fR is an array of
159 buffers where the public key encrypted secret key will be written, each buffer
160 must contain enough room for the corresponding encrypted key: that is
161 \&\fBek[i]\fR must have room for \fBEVP_PKEY_size(pubk[i])\fR bytes. The actual
162 size of each encrypted secret key is written to the array \fBekl\fR. \fBpubk\fR is
163 an array of \fBnpubk\fR public keys.
164 .PP
165 The \fBiv\fR parameter is a buffer where the generated \s-1IV\s0 is written to. It must
166 contain enough room for the corresponding cipher's \s-1IV\s0, as determined by (for
167 example) EVP_CIPHER_iv_length(type).
168 .PP
169 If the cipher does not require an \s-1IV\s0 then the \fBiv\fR parameter is ignored
170 and can be \fB\s-1NULL\s0\fR.
171 .PP
172 \&\fIEVP_SealUpdate()\fR and \fIEVP_SealFinal()\fR have exactly the same properties
173 as the \fIEVP_EncryptUpdate()\fR and \fIEVP_EncryptFinal()\fR routines, as
174 documented on the \fIEVP_EncryptInit\fR\|(3) manual
175 page.
176 .SH "RETURN VALUES"
177 .IX Header "RETURN VALUES"
178 \&\fIEVP_SealInit()\fR returns 0 on error or \fBnpubk\fR if successful.
179 .PP
180 \&\fIEVP_SealUpdate()\fR and \fIEVP_SealFinal()\fR return 1 for success and 0 for
181 failure.
182 .SH "NOTES"
183 .IX Header "NOTES"
184 Because a random secret key is generated the random number generator
185 must be seeded before calling \fIEVP_SealInit()\fR.
186 .PP
187 The public key must be \s-1RSA\s0 because it is the only OpenSSL public key
188 algorithm that supports key transport.
189 .PP
190 Envelope encryption is the usual method of using public key encryption
191 on large amounts of data, this is because public key encryption is slow
192 but symmetric encryption is fast. So symmetric encryption is used for
193 bulk encryption and the small random symmetric key used is transferred
194 using public key encryption.
195 .PP
196 It is possible to call \fIEVP_SealInit()\fR twice in the same way as
197 \&\fIEVP_EncryptInit()\fR. The first call should have \fBnpubk\fR set to 0
198 and (after setting any cipher parameters) it should be called again
199 with \fBtype\fR set to \s-1NULL\s0.
200 .SH "SEE ALSO"
201 .IX Header "SEE ALSO"
202 \&\fIevp\fR\|(3), \fIrand\fR\|(3),
203 \&\fIEVP_EncryptInit\fR\|(3),
204 \&\fIEVP_OpenInit\fR\|(3)
205 .SH "HISTORY"
206 .IX Header "HISTORY"
207 \&\fIEVP_SealFinal()\fR did not return a value before OpenSSL 0.9.7.