Logstash cipher filter issue


I'm encrypting some data using logstash cipher filter & store the encrypted data in elasticsearch. The code snippet used for the encryption is as follow:
filter {
cipher {
algorithm => "aes-256-cbc"
cipher_padding => 1
iv_random_length => 16
key => "<32_DIGITS_KEY>"
key_size => 32
mode => "encrypt"
source => "[message]"
target => "[message_enc]"

When I read the data from this elasticsearch index using java code & decrypt it then I'm getting same random unicode string before my actual data. Sample random string is "r��1�><��B9c�M**<MY_STRING>**"

I didn't find anything in my code to resolve this issue.

Please help me in resolving this.