ASR

C47360ry: Cryp706r4phy

P01n75: 50

D35cr1p710n: Déch1ffr3z c3 m355463 !

F1l35: pub.key 3nc

TL;DR

An 4774ck 0n 7h3 pu8l1c k3y 4ll0w5 u5 70 f1nd 7h3 pr1v473 k3y 4nd d3cryp7 7h3 fl46.

M37h0d0l06y

>_ file pub.key enc
pub.key: ASCII text
enc:     data

>_ cat pub.key
-----BEGIN PUBLIC KEY-----
MIIBHzANBgkqhkiG9w0BAQEFAAOCAQwAMIIBBwKBgQFhlIOluuAcFAdBWvfwKUwI
P71JK3mocBEII+GDY1czp3IPiKQvVnIraRjLqkpfyp+0dVTwIAoNlxZD0Vc4k6eh
7Bga34NysEtB1m9FT3Sp89juKpz2ubGByvCb1JBj/pHoIauOMHB6GsI5f1Lkk0dx
XHN2JkzEXHJ9HGlhq/OjEQKBgF3Nn1FtKmfSliDjEEuS289r7i/UOQkA3IfjkriG
u7DFLSRz9Lv/lILOP9yCGa5CwN5GGXOFjyTzBN9YORRt8t7pSj4BP9TUoEV4WXSp
FemEdMizhIlEc+p5UP1siva5V7+2P33x5N8p+H+a6l7G/4eTbF6cDBxvLEYJLJ+k
sGqJ
-----END PUBLIC KEY-----

>_ cat enc
8�X5?��5u2_*�_j���
r~�B�L�?��$��F"\�(�:��]��nˏ���

R34d1n6 7h3 717l3, 17 500n 83c0m35 cl34r 7h47 w3 4r3 d34l1n6 w17h RSA !

S0 w3 h4v3 70 r3c0v3r 7h3 m355463 8u7 w3 d0n'7 h4v3 7h3 pr1v473 k3y (17 w0uld 83 700 345y).

Th3 57473m3n7 54y5 "Déch1ffr3z" 4nd n07 "Décryp73r" (1n fr3nch 7h3r3 15 4 d1ff3r3nc3 ;) I7 m34n5 7h47 w3 c4n r3c0v3r 7h3 pr1v473 k3y u51n6 7h3 pu8l1c k3y.

S0 w3'r3 601n6 70 7ry 70 f1nd 7h3 pr1v473 k3y u51n6 0ur pu8l1c k3y.

RsaCtfTool 15 u53ful 70 d0 7h47 :)

>_ ./RsaCtfTool/RsaCtfTool.py --publickey pub.key --private
-----BEGIN RSA PRIVATE KEY-----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-----END RSA PRIVATE KEY-----

P3rf3c7, w3'v3 607 0ur pr1v473 k3y. N0w d3cryp7 7h3 m355463.

Alw4y5 w17h RsaCtfTool

>_ ./RsaCtfTool/RsaCtfTool.py --publickey pub.key --uncipherfile enc
[+] Clear text : b'\x00\x02L\x80\xf7\xda\x832\xc2\xa9\x01\xdc\xff\x01\x0b\xb3\x05\x83Ak\x7f\xa48o\xf6\xbek\xe2:\xb6\x1f5\x19{\x1b\x99\xf9\xf9\xd4\xfe\xb4\xd5\xbc!e\x85\x0f\x83Q\xd8\xcf\x16\x19\xbbZ\xc6)F\xf4\xfc\xa7\xfd\xe1,\xe8D\xef\xb5\x02\x16\x81\xfd4\x0c\x16:]ZK\xcf\xc7\x8b\xfbx\xaf\xe1\x00BREIZHCTF{RSA_may_be_sometimes_vulnerable}'

FLAG_IS:

BREIZHCTF{RSA_m4y_83_50m371m35_vuln3r48l3}