For these purposes, will work well [RsaCtfTool](https://github.com/sourcekris/RsaCtfTool)

```
cd /opt/RsaCtfTool
./RsaCtfTool.py --publickey /media/DATA/CTF/yubitsec/RSA_I/RSA/Part1/PublicKey1.pem --private --uncipher /media/DATA/CTF/yubitsec/RSA_I/RSA/Part1/ciphertext1
./RsaCtfTool.py --publickey /media/DATA/CTF/yubitsec/RSA_I/RSA/Part2/PublicKey2.pem --private --uncipher /media/DATA/CTF/yubitsec/RSA_I/RSA/Part2/ciphertext2
./RsaCtfTool.py --publickey /media/DATA/CTF/yubitsec/RSA_I/RSA/Part3/PublicKey3.pem --private --uncipher /media/DATA/CTF/yubitsec/RSA_I/RSA/Part3/ciphertext3
```
After the launch it only remains to collect the flag:
```
gh0st3rs@leacher-pc:RSA_I$ ./solver.sh
-----BEGIN RSA PRIVATE KEY-----
MG4CAQACExqs08kNGr393d4YNfWKiPA2i58CAwEAAQITAQtEmrjVlBwMg4SswXPA
D6tZMQIKA15X18VLlSZm6QIKB+s+al7J1uFZRwIKAJ2AqdZNQcar0QIKAJDL53sX
vZJg9wIKAuJxXfZGtKRLsg==
-----END RSA PRIVATE KEY-----
[+] Clear text : ?�ԗ��tA?3�YUBITS
-----BEGIN RSA PRIVATE KEY-----
MG8CAQACFAOK8x5ZjiQrX88bMG/f8OLWbvI5AgMBAAECEyglbOF/9j/pRMn/kooJ
wOtYVoUCCh1itmCUgFlKT/8CCh7dHr/XqtdlPccCCgt2f0hLhYnPSEcCChb4x+lM
UZlOfoMCCg0EYHu6Sip/N/s=
-----END RSA PRIVATE KEY-----
[+] Clear text : ?�6x?A�KΡEC{S4V3
-----BEGIN RSA PRIVATE KEY-----
MG4CAQACE2V6kIQmEBr6JVHPyibjmvVkUycCAwEAAQITQyZ6kOe7Co7yqrRYsOVc
BFCU0QIKBs3zoRJ7rHVf6QIKDunZ8G691p3AjwIKA6M+x7F15HCrYQIKBBzmJ/LC
lB+pbQIKA1rNqY0KXkCtvg==
-----END RSA PRIVATE KEY-----
[+] Clear text : ?�"?Ꙍ���_FL46}
```

Flag: YUBITSEC{S4V3_FL46}