215 lines
7.1 KiB
Groff
215 lines
7.1 KiB
Groff
.\" $NetBSD: EVP_SealInit.3,v 1.16 2005/11/25 21:09:34 christos Exp $
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.\" ========================================================================
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.\"
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.IX Title "EVP_SealInit 3"
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.TH EVP_SealInit 3 "2005-11-24" "0.9.8a" "OpenSSL"
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.SH "NAME"
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EVP_SealInit, EVP_SealUpdate, EVP_SealFinal \- EVP envelope encryption
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.SH "LIBRARY"
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libcrypto, -lcrypto
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.SH "SYNOPSIS"
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.IX Header "SYNOPSIS"
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.Vb 1
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\& #include <openssl/evp.h>
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.Ve
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.PP
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.Vb 7
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\& int EVP_SealInit(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type,
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\& unsigned char **ek, int *ekl, unsigned char *iv,
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\& EVP_PKEY **pubk, int npubk);
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\& int EVP_SealUpdate(EVP_CIPHER_CTX *ctx, unsigned char *out,
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\& int *outl, unsigned char *in, int inl);
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\& int EVP_SealFinal(EVP_CIPHER_CTX *ctx, unsigned char *out,
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\& int *outl);
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.Ve
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.SH "DESCRIPTION"
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.IX Header "DESCRIPTION"
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The \s-1EVP\s0 envelope routines are a high level interface to envelope
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encryption. They generate a random key and \s-1IV\s0 (if required) then
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\&\*(L"envelope\*(R" it by using public key encryption. Data can then be
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encrypted using this key.
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.PP
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\&\fIEVP_SealInit()\fR initializes a cipher context \fBctx\fR for encryption
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with cipher \fBtype\fR using a random secret key and \s-1IV\s0. \fBtype\fR is normally
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supplied by a function such as \fIEVP_des_cbc()\fR. The secret key is encrypted
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using one or more public keys, this allows the same encrypted data to be
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decrypted using any of the corresponding private keys. \fBek\fR is an array of
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buffers where the public key encrypted secret key will be written, each buffer
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must contain enough room for the corresponding encrypted key: that is
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\&\fBek[i]\fR must have room for \fBEVP_PKEY_size(pubk[i])\fR bytes. The actual
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size of each encrypted secret key is written to the array \fBekl\fR. \fBpubk\fR is
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an array of \fBnpubk\fR public keys.
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.PP
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The \fBiv\fR parameter is a buffer where the generated \s-1IV\s0 is written to. It must
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contain enough room for the corresponding cipher's \s-1IV\s0, as determined by (for
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example) EVP_CIPHER_iv_length(type).
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.PP
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If the cipher does not require an \s-1IV\s0 then the \fBiv\fR parameter is ignored
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and can be \fB\s-1NULL\s0\fR.
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.PP
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\&\fIEVP_SealUpdate()\fR and \fIEVP_SealFinal()\fR have exactly the same properties
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as the \fIEVP_EncryptUpdate()\fR and \fIEVP_EncryptFinal()\fR routines, as
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documented on the \fIEVP_EncryptInit\fR\|(3) manual
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page.
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.SH "RETURN VALUES"
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.IX Header "RETURN VALUES"
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\&\fIEVP_SealInit()\fR returns 0 on error or \fBnpubk\fR if successful.
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.PP
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\&\fIEVP_SealUpdate()\fR and \fIEVP_SealFinal()\fR return 1 for success and 0 for
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failure.
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.SH "NOTES"
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.IX Header "NOTES"
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Because a random secret key is generated the random number generator
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must be seeded before calling \fIEVP_SealInit()\fR.
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.PP
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The public key must be \s-1RSA\s0 because it is the only OpenSSL public key
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algorithm that supports key transport.
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.PP
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Envelope encryption is the usual method of using public key encryption
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on large amounts of data, this is because public key encryption is slow
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but symmetric encryption is fast. So symmetric encryption is used for
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bulk encryption and the small random symmetric key used is transferred
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using public key encryption.
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.PP
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It is possible to call \fIEVP_SealInit()\fR twice in the same way as
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\&\fIEVP_EncryptInit()\fR. The first call should have \fBnpubk\fR set to 0
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and (after setting any cipher parameters) it should be called again
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with \fBtype\fR set to \s-1NULL\s0.
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.SH "SEE ALSO"
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.IX Header "SEE ALSO"
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\&\fIevp\fR\|(3), \fIrand\fR\|(3),
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\&\fIEVP_EncryptInit\fR\|(3),
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\&\fIEVP_OpenInit\fR\|(3)
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.SH "HISTORY"
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.IX Header "HISTORY"
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\&\fIEVP_SealFinal()\fR did not return a value before OpenSSL 0.9.7.
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