Functions provided by the Entrust PostgreSQL Extension

open_session()
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```
open_session(access token file path) returns void

open_session(access token) returns void
```
The open_session() function is responsible for creating a session. It reads the access token either from a file or directly as a parameter. Once the access token is obtained, the function stores it in cache for subsequent use.

For example:
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```
select open_session('file:///opt/hcs/etc/psql.conf');
```
close_session()
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```
close_session() returns void
```
The close_session() function is used to close a session. This function will remove the access token and keys from the cache.

For example:
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```
select close_session();
```
get_key()
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```
get_key(keyname) returns key handle (INTEGER)
```
The get_key() function is used to fetch a key from the Cryptographic Security Platform Vault for Databases. It stores the key in the cache and returns the key handle.

For example:
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```
select get_key('master-key1') as handle \gset
```
encrypt_data(text, key_handle)
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```
encrypt_data(data TEXT, keyhandle INTEGER) returns TEXT
```
The encrypt_data() function is used to encrypt the provided TEXT type data. It has two parameters: data and key_handle. The key_handle is returned by the get_key() function. It returns encrypted TEXT data.

For example:
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```
insert into users (name, credit_card_details) values ('John', encrypt_data('my_details', :handle));
```
decrypt_data()
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```
decrypt_data(encrypted_data TEXT) returns TEXT
```
The decrypt_data() function is used to decrypt TEXT type data. It also verifies the integrity of the data during decryption. It returns decrypted TEXT data.

For example:
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```
select name, decrypt_data(credit_card_details) from users;
```
encrypt_data_bytea()
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```
encrypt_data_bytea(data BYTEA, keyhandle INTEGER) returns BYTEA
```
The encrypt_data_bytea() function is used to encrypt the provided BYTEA type data. It has two parameters: data and key_handle. The key_handle is returned by the get_key() function. It returns encrypted BYTEA data.

For example:
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```
insert into users (name, bytea_details) values ('John', encrypt_data_bytea(E'\\xDEADBEEF', :handle));
```
decrypt_data_bytea()
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```
decrypt_data_bytea(encrypted_data BYTEA) returns BYTEA
```
The decrypt_data_bytea() function is used to decrypt BYTEA data. It also verifies the integrity of the data during decryption. It returns decrypted BYTEA data.

For example:
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```
select name, decrypt_data_bytea(bytea_details) from users;
```