Solved

Public / Private keys

Posted on 2014-04-02
3
257 Views
Last Modified: 2014-04-03
Can you  have the following

1> 1 to many relationship between a private key and a public key

2> A one to many relationship between a public key and a private key
0
Comment
Question by:Anthony Lucia
  • 2
3 Comments
 
LVL 33

Accepted Solution

by:
Dave Howe earned 500 total points
ID: 39973624
Sort of.

Extended version? there is a mathematical relationship between the two keys such that given the original constants and one of the keys, you can compute the other.

For RSA, that is such that for the three values M (modulus), E (encryption exponent) and D (decryption exponent) then cryptotext=plaintext to the power of E modulo M, and plaintext = cryptotext to the power of D modulo M. this is reversible, in that if you swap E and D over, the math still works.

however, for any pair (E,M) there are an infinite number of possible values for D, all with a rigid mathematical relationship to each other. You don't HAVE to pick the smallest one, but it usually makes sense to do so (as otherwise you are just doing more math for no real benefit)

Summary of RSA would go like this (and I have a t-shirt with this on someplace here :)

Pick two prime numbers P and Q
Your M is the value P x Q
now, pick an E (say, 512) and calculate N as the value (P - 1) x (Q - 1)
Now, any D such that E x D = 1 Mod N is suitable.

now, given you can write "Mod N" as "i x N" for some arbitrary integer i you can rearrange that so that for any given value i, you can calculate the resulting D value.

conversely, if you have calculated some D, you can go ahead and calculate other values of E by varying the value of i.

Does that make sense?
0
 
LVL 38

Expert Comment

by:Rich Rumble
ID: 39976472
Your thinking of the web of trust, or the method used in SMIME/PGP where one can encrypt the massage once, but send the same message to a handful of people. The way that works is, the public key of the recipients (each of them) is used to encrypt the same string (string_x). When they recieve the message they use their private-keys to decrypt string_x, and then string_x to decrypt the message itself.
MS EFS works in this way as well, where each users public-key is used to encrypt the file-encryption-key (string_x), and the FEK is used to encrypt the data.
Basically mixing asymmetric and symmetric encryption types.
-rich
0
 
LVL 33

Expert Comment

by:Dave Howe
ID: 39976534
Its possible he is thinking that. Not sure I can tell any more what he is thinking, given the storm of questions :)

Gotta love DESX though. I wonder why it wasn't used outside of EFS?
0

Featured Post

Ransomware-A Revenue Bonanza for Service Providers

Ransomware – malware that gets on your customers’ computers, encrypts their data, and extorts a hefty ransom for the decryption keys – is a surging new threat.  The purpose of this eBook is to educate the reader about ransomware attacks.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

Title # Comments Views Activity
Windows 10 4 39
Best way of mitigating threat from USB flash drives 9 93
Successful Penetration Tests case study 3 58
forensics tools for file amendments/associations 2 63
Find out what Office 365 Transport Rules are, how they work and their limitations managing Office 365 signatures.
There are many Password Managers (PM) out there to choose from. PM's can help with your password habits and routines, but they should not be a crutch you rely on too heavily. I also have an article for company/enterprise PM's.
Sending a Secure fax is easy with eFax Corporate (http://www.enterprise.efax.com). First, Just open a new email message.  In the To field, type your recipient's fax number @efaxsend.com. You can even send a secure international fax — just include t…
A simple description of email encryption using a secure portal service. This is one of the choices offered by The Email Laundry for email encryption. The other choices are pdf encryption which creates an encrypted pdf of your email and any attachmen…

911 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

20 Experts available now in Live!

Get 1:1 Help Now