Used private key:
-----BEGIN PRIVATE KEY-----
MIIBDAIBADANBgkqhkiG9w0BAQEFAASB9zCB9AIBAAIxAMAyyOArE+BoIgN+pipy
f5uki64O8Grs5Kf6LrBo45Ik7KIlYhn8OJ+kzlz2dhYoDQIDAQABAjEAp8ruYf5Z
sP1YTJLCAKbLTxc9Nq0mKUM76eS8wLEz+pfnQaWnis6cUizlq58ALGKBAhkA/Nka
cyMvIVxWQFrGJSOQFR62BGrKyP5tAhkAwpgiWXqSHmSz40wmV3FDtUVSE3xGGUwh
AhkAiuM6aypVdi7BVgJGuxnIyEEhXFXI5BUVAhhhFDK2vw5ceVLBB4FtSEVGDrI2
pF34SuECGQCARpqFXpLNRAjjFpdt6GeRGpnpt0MkCOc=
-----END PRIVATE KEY-----

You can use the query string to specify the data (base64 encoded)
Decrypted text: Y3ONep46Uwf9NfRkF1cmyphU9RWhUIIUuU1RP/4luTuw9QiQcrzxldnqjlrTy4nq
Decrypted content:
1234567890123456789012345678901234567
This decryption uses a pre-defined key pair.