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Ron Teitelbaum

Help with RSA

Hello All,

I’m working on SSL / TLS implementation in Squeak and I need some help understanding RSA.

It appears that our RSA implementation has an encodingParameter. I see what it’s doing but now I’m confused and was hoping that someone could explain this to me.

I see that the parameter is needs to be the same for encrypting and decrypting, or it doesn’t work.

My question is how is this stored on a certificate?

Here is the MS Export format http://msdn.microsoft.com/library/default.asp?url=/library/en-us/seccrypto/security/private_key_blobs.asp

Field	Description
blobheader	A BLOBHEADER structure as described in a previous section. The bType field must always have a value of PRIVATEKEYBLOB.
rsapubkey	A RSAPUBKEY structure as described in Public Key BLOBs. The magic field must always have a value of 0x32415352 ("RSA2").
modulus	The modulus. This has a value of "prime1 * prime2" and is often known as "n".
prime1	Prime number 1, often known as "p".
prime2	Prime number 2, often known as "q".
exponent1	Exponent 1. This has a numeric value of "d mod (p - 1)".
exponent2	Exponent 2. This has a numeric value of "d mod (q - 1)".
coefficient	Coefficient. This has a numeric value of "(inverse of q) mod p".
privateExponent	Private exponent, often known as "d".

I also noticed that : http://en.wikipedia.org/wiki/RSA

For reasons of efficiency sometimes a different form of the private key (including CRT parameters) is stored:

p and q, the primes from the key generation,
d mod (p-1) and d mod (q-1) (often known as dmp1 and dmq1)
(1/q) mod p (often known as iqmp)

Does this mean that the parameter is the coefficient? Is the CRT parameter the encoding parameter? Any help would be very much appreciated, I’m having trouble understanding the differences, and how the parameter is supposed to be used.

Thanks!

Ron Teitelbaum

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Ron Teitelbaum

RE: Help with RSA

Thank you Matt!

Ron

From: Matthew S. Hamrick [mailto:[hidden email]]
Sent: Thursday, August 17, 2006 3:09 AM
To: Ron Teitelbaum
Subject: Re: [Cryptography Team] Help with RSA

Hey Ron...

I haven't been looking too closely at the official crypto source, so I can't say for sure. But from the sound of it, maybe it's the message encoding scheme for the RSA signature. There are two main encoding schemes: PKCS#1 and OAEP, though PKCS#1 now includes OAEP as an option. There's also ISO9697, but I've never seen it used in conjunction with X.509. If this is the encoding scheme, then it can be found in the ALGO oid in the SubjectPublicKeyInfo portion of the cert.

Hope this helps.

-Cheers

-Matt H.

On Aug 16, 2006, at 8:21 PM, Ron Teitelbaum wrote:

Hello All,

I’m working on SSL / TLS implementation in Squeak and I need some help understanding RSA.

It appears that our RSA implementation has an encodingParameter. I see what it’s doing but now I’m confused and was hoping that someone could explain this to me.

I see that the parameter is needs to be the same for encrypting and decrypting, or it doesn’t work.

My question is how is this stored on a certificate?

Here is the MS Export format http://msdn.microsoft.com/library/default.asp?url=/library/en-us/seccrypto/security/private_key_blobs.asp

Field	Description
blobheader	A BLOBHEADER structure as described in a previous section. The bType field must always have a value of PRIVATEKEYBLOB.
rsapubkey	A RSAPUBKEY structure as described in Public Key BLOBs. The magic field must always have a value of 0x32415352 ("RSA2").
modulus	The modulus. This has a value of "prime1 * prime2" and is often known as "n".
prime1	Prime number 1, often known as "p".
prime2	Prime number 2, often known as "q".
exponent1	Exponent 1. This has a numeric value of "d mod (p - 1)".
exponent2	Exponent 2. This has a numeric value of "d mod (q - 1)".
coefficient	Coefficient. This has a numeric value of "(inverse of q) mod p".
privateExponent	Private exponent, often known as "d".

I also noticed that : http://en.wikipedia.org/wiki/RSA

For reasons of efficiency sometimes a different form of the private key (including CRT parameters) is stored:

p and q, the primes from the key generation,
d mod (p-1) and d mod (q-1) (often known as dmp1 and dmq1)
(1/q) mod p (often known as iqmp)

Thanks!

Ron Teitelbaum

_______________________________________________

Cryptography mailing list

[hidden email]

http://lists.squeakfoundation.org/cgi-bin/mailman/listinfo/cryptography

_______________________________________________
Cryptography mailing list
[hidden email]
http://lists.squeakfoundation.org/cgi-bin/mailman/listinfo/cryptography