Misdirection Again (Why am I not surprised?)
So.....in Public Key Cryptography there's a public key (duh!) and the owner of that public key also has a private key (secret....not public). So messages using this key pair can be attacked in two different ways......the keys can be attacked, or the messages can be attacked, or both.
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In Symmetrical Key Cryptography there's a secret key, used by both the sender and the recipient of a message. So any attack boils down to guessing the key. (Of course the snoops might try to STEAL the key too...but that's cheating!!).
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And finally, there may be people who use a cryptography algorithm which is not published, but which might (or might not) be a variant of one of the published algorithms. In this case, it's not at all clear whether ANY type of attack might be possible......because for ANY attack to be designed, the algorithm needs to be known. Quantum computers may be good at guessing keys......but the guesses have to be applied to the encrypted message USING AN ALGORITHM!
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Just as a little test, here's a message using a private algorithm. El Reg readers with access to a quantum computer are welcome to publish the plain text in a prompt reply!
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uv2JG5ef4PcVi1mzCh2Ns54L8T0R6VqNihSR2XqNoxyxINgZwRoZOV2paXSNWvcVWjwXiNgfKNiJ
eXYVW3ulCHujGXE1gDyl4dOHQN2nc5O3ElKNk907KfmrKDQnkDo1U5UFCFIroTURqREFUVUhqD2z
YZ4Rgdul0JqhiJSNC5yZ6tMluno3ePaRklwx674b07SjIJuZ8ZyfePYxOHqTCPY3a1M9KdWj0TQz
YBG5glQ3uv8BsTW5sdaLC5mdufIfYdKJa7CBqFSfqTw94t0BcfKvyz4RydKDSXgLMTWtkXUVgXUn
6bGZ0jOZY1OfgvM1mhCxMfSPgX0rqB8naDK36D4Ze5I7eRW14TglwFg3E9cTMjoVs9AJyFwjOReH
G5o50ZKviXCJYjiFQ7apUXwdIdwR6Z09UFkLAXghm3yjELQXgNQp63gPSBEDKbAVqNOLOBUJcNwr
Q5uhwlgD0vWrkrkLuPYZ4f2j0xmn0ZWt0juxU5ipsRwTqL4hevYby5UJmhIVu5WH81YXit8doTSV
6501gNqvIrCjqRMHKHghiHm5k9YpsFA7iJadkrGBGdIN2BIbA7SbgVQ7UPMtylwfohKh8325I9Ib
WpGn4LStSTmfMtuPaFUNIDCLAhCNQjEhE58peb2TelEfcP29mrspGpcTENOTwvy50jS7ijwXgdG3
Uvo7YxQ3aLy7cLm5qfStSzIdk1slG9Cp6vwLAbmVMNGLkrMj2R6XyzyVotsjChY9WfEjg9KvWlSp
obwhQ1QFUtubS58VIb2v8v6bubsZcnopGV85Y1Mhe70XKbKF6pYLCDgh0dMpOnml8rEDmDaNY9Mr
QlQ1Yb0VSRkvs1Wn6t0FilMJepupoLUN8FcjGNU7y14rStQJUB0PE1GTgJWHUnQ7AtiHQDeb0l8h
8D2JYzibGjMXYNWte5azAbczgL6faHEZ0dMTEb2tOREvONmXUDAJeVsR6hQFgtm3UBi5kfuFef67
oR0vKhITmPA9C74v0jIXSfcLo307QhyziD4dGNqFwHIlkXIPinKFiX0P4R4VI90dSHYJUvKHStCl
c98BqR61ihoRg7kHOTubAfAx8jAzYvevepQFgNsVkdsRoNeZUvGxUn4DCD0dK3WHqNOPWrQfYjmz
gz4jMBwzq7i5an2Nev632RUHQbazEPoFUdKNIRIZsNm3i3MTs5ELWv8hClMtIJIJIFsLmP6BSnG3
UhApUDOJCjgVK16Vc9EF2b8z0d09k507K3KFW1yHqX4rE9spyr0dSTWnmfw5IZYp4Tup2NSz6z2x
kV6foPkdmt0Za34ROfuHyfUfm5kd8HGJGnqZyBOx0pAhITUZI3QBW7QhYhcNspg7wnUhI325KTu1
GTAt8ngfsdsxYjY34ZO9S7EXmpE7KT6zC34dOD65EXuxEFAHS9Ov6r6ZGTQtGFkZEfAPu7OpIna7
CRWp4HuhUL0LstG3KtklqPgBsfgLghsfW3wFG3QNYNgjmjqneRmFOHMzQhS9gzINWrW1MBmt2H8D
I1KdaXoL6NKNwvwlopuxMxArwjWZw1Kdij4ruxcVyD4pE90foD4xO7gPEFEn6RSl8PqnCFOFyTmF
EruLgN0f05W7I5CvKpG5svePS7ItglqP0p4V0v0ni945YxGnCdwBIHUBMJ2By5If6vgxkD8hGbMn
O3krCzIV4dGliHCXExw9OFsXqN6FmlKPGL87Ej43IHMz6zop0vcjQbC9c1CHqvqXUbkRYbClS7gH
29qjKBMJo5Mj43kt8HMzmPobilsJi76tenaPqjMxGdCF4ZEbuJIvCXgXqV0JERyrqB6XcP6P
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Hint.....before you start, you might like to consider whether this really is base64!