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1 | =pod | ||
2 | |||
3 | =head1 NAME | ||
4 | |||
5 | EVP_SealInit, EVP_SealUpdate, EVP_SealFinal - EVP envelope encryption | ||
6 | |||
7 | =head1 SYNOPSIS | ||
8 | |||
9 | #include <openssl/evp.h> | ||
10 | |||
11 | int EVP_SealInit(EVP_CIPHER_CTX *ctx, EVP_CIPHER *type, unsigned char **ek, | ||
12 | int *ekl, unsigned char *iv,EVP_PKEY **pubk, int npubk); | ||
13 | int EVP_SealUpdate(EVP_CIPHER_CTX *ctx, unsigned char *out, | ||
14 | int *outl, unsigned char *in, int inl); | ||
15 | int EVP_SealFinal(EVP_CIPHER_CTX *ctx, unsigned char *out, | ||
16 | int *outl); | ||
17 | |||
18 | =head1 DESCRIPTION | ||
19 | |||
20 | The EVP envelope routines are a high level interface to envelope | ||
21 | encryption. They generate a random key and then "envelope" it by | ||
22 | using public key encryption. Data can then be encrypted using this | ||
23 | key. | ||
24 | |||
25 | EVP_SealInit() initializes a cipher context B<ctx> for encryption | ||
26 | with cipher B<type> using a random secret key and IV supplied in | ||
27 | the B<iv> parameter. B<type> is normally supplied by a function such | ||
28 | as EVP_des_cbc(). The secret key is encrypted using one or more public | ||
29 | keys, this allows the same encrypted data to be decrypted using any | ||
30 | of the corresponding private keys. B<ek> is an array of buffers where | ||
31 | the public key encrypted secret key will be written, each buffer must | ||
32 | contain enough room for the corresponding encrypted key: that is | ||
33 | B<ek[i]> must have room for B<EVP_PKEY_size(pubk[i])> bytes. The actual | ||
34 | size of each encrypted secret key is written to the array B<ekl>. B<pubk> is | ||
35 | an array of B<npubk> public keys. | ||
36 | |||
37 | EVP_SealUpdate() and EVP_SealFinal() have exactly the same properties | ||
38 | as the EVP_EncryptUpdate() and EVP_EncryptFinal() routines, as | ||
39 | documented on the L<EVP_EncryptInit(3)|EVP_EncryptInit(3)> manual | ||
40 | page. | ||
41 | |||
42 | =head1 RETURN VALUES | ||
43 | |||
44 | EVP_SealInit() returns 0 on error or B<npubk> if successful. | ||
45 | |||
46 | EVP_SealUpdate() and EVP_SealFinal() return 1 for success and 0 for | ||
47 | failure. | ||
48 | |||
49 | =head1 NOTES | ||
50 | |||
51 | Because a random secret key is generated the random number generator | ||
52 | must be seeded before calling EVP_SealInit(). | ||
53 | |||
54 | The public key must be RSA because it is the only OpenSSL public key | ||
55 | algorithm that supports key transport. | ||
56 | |||
57 | Envelope encryption is the usual method of using public key encryption | ||
58 | on large amounts of data, this is because public key encryption is slow | ||
59 | but symmetric encryption is fast. So symmetric encryption is used for | ||
60 | bulk encryption and the small random symmetric key used is transferred | ||
61 | using public key encryption. | ||
62 | |||
63 | It is possible to call EVP_SealInit() twice in the same way as | ||
64 | EVP_EncryptInit(). The first call should have B<npubk> set to 0 | ||
65 | and (after setting any cipher parameters) it should be called again | ||
66 | with B<type> set to NULL. | ||
67 | |||
68 | =head1 SEE ALSO | ||
69 | |||
70 | L<evp(3)|evp(3)>, L<rand(3)|rand(3)>, | ||
71 | L<EVP_EncryptInit(3)|EVP_EncryptInit(3)>, | ||
72 | L<EVP_OpenInit(3)|EVP_OpenInit(3)> | ||
73 | |||
74 | =head1 HISTORY | ||
75 | |||
76 | =cut | ||