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NAME

     EVP_SealInit, EVP_SealUpdate, EVP_SealFinal - EVP envelope
     encryption



SYNOPSIS
      #include <openssl/evp.h>

      int EVP_SealInit(EVP_CIPHER_CTX *ctx, EVP_CIPHER *type, unsigned char **ek,
                     int *ekl, unsigned char *iv,EVP_PKEY **pubk, int npubk);
      int EVP_SealUpdate(EVP_CIPHER_CTX *ctx, unsigned char *out,
              int *outl, unsigned char *in, int inl);
      int EVP_SealFinal(EVP_CIPHER_CTX *ctx, unsigned char *out,
              int *outl);




DESCRIPTION
     The EVP envelope routines are a high level interface to
     envelope encryption. They generate a random key and then
     "envelope" it by using public key encryption. Data can then
     be encrypted using this key.

     EVP_SealInit() initializes a cipher context ctx for
     encryption with cipher type using a random secret key and IV
     supplied in the iv parameter. type is normally supplied by a
     function such as EVP_des_cbc(). The secret key is encrypted
     using one or more public keys, this allows the same
     encrypted data to be decrypted using any of the
     corresponding private keys. ek is an array of buffers where
     the public key encrypted secret key will be written, each
     buffer must contain enough room for the corresponding
     encrypted key: that is ek[i] must have room for
     EVP_PKEY_size(pubk[i]) bytes. The actual size of each
     encrypted secret key is written to the array ekl. pubk is an
     array of npubk public keys.

     EVP_SealUpdate() and EVP_SealFinal() have exactly the same
     properties as the EVP_EncryptUpdate() and EVP_EncryptFinal()
     routines, as documented on the EVP_EncryptInit(3) manual
     page.



RETURN VALUES
     EVP_SealInit() returns 0 on error or npubk if successful.

     EVP_SealUpdate() and EVP_SealFinal() return 1 for success
     and 0 for failure.



NOTES
     Because a random secret key is generated the random number
     generator must be seeded before calling EVP_SealInit().

     The public key must be RSA because it is the only OpenSSL
     public key algorithm that supports key transport.
     Envelope encryption is the usual method of using public key
     encryption on large amounts of data, this is because public
     key encryption is slow but symmetric encryption is fast. So
     symmetric encryption is used for bulk encryption and the
     small random symmetric key used is transferred using public
     key encryption.

     It is possible to call EVP_SealInit() twice in the same way
     as EVP_EncryptInit(). The first call should have npubk set
     to 0 and (after setting any cipher parameters) it should be
     called again with type set to NULL.



SEE ALSO
     evp(3), rand(3), EVP_EncryptInit(3), EVP_OpenInit(3)



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Created 1996-2024 by Maxim Chirkov

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