---
name: "libressl-EVP_SealInit"
section: "3"
platform: "linux"
package: "libressl"
version: "4.4.0-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/libressl-EVP_SealInit"
---

# libressl-EVP\_SealInit(3)

EVP envelope encryption

## NAME

**EVP\_SealInit**, **EVP\_SealUpdate**, **EVP\_SealFinal** – EVP envelope encryption

## SYNOPSIS

Crypto Library (libcrypto, -lcrypto)

**#include \<openssl/evp.h\>**

*int*\

**EVP\_SealInit**(*EVP\_CIPHER\_CTX \*ctx*, *const 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 IV (if required) 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. *type* is normally supplied by a function such as EVP\_aes\_256\_cbc(3); see EVP\_EncryptInit(3) for details. 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.

The *iv* parameter is a buffer where the generated IV is written to. It must contain enough room for the corresponding cipher's IV, as determined by (for example) **EVP\_CIPHER\_iv\_length**(*type*).

If the cipher does not require an IV then the *iv* parameter is ignored and can be NULL.

**EVP\_SealUpdate**() and **EVP\_SealFinal**() have exactly the same properties as the EVP\_EncryptUpdate(3) and EVP\_EncryptFinal(3) routines.

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(3). 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.

**EVP\_SealUpdate**() is implemented as a macro.

## RETURN VALUES

**EVP\_SealInit**() usually returns 0 on error or *npubk* if successful. If **EVP\_SealInit**() is called with *npubk* set to 0 or with *pubk* set to NULL, it returns 1 for success and 0 for failure.

**EVP\_SealUpdate**() and **EVP\_SealFinal**() return 1 for success and 0 for failure.

## SEE ALSO

evp(3), EVP\_EncryptInit(3), EVP\_OpenInit(3)

## HISTORY

**EVP\_SealInit**(), **EVP\_SealUpdate**(), and **EVP\_SealFinal**() first appeared in SSLeay 0.5.1 and have been available since OpenBSD 2.4.

**EVP\_SealFinal**() did not return a value before OpenSSL 0.9.7.