Re: Hash of Public key
From: Valery Pryamikov (valery_at_harper.no)
Date: 05/23/05
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Date: Mon, 23 May 2005 12:42:07 +0200
Just a minor correction - it's DumpASN utility (not ASNDump as I wrote in my
prev.post)
-Valery.
http://www.harper.no/valery
"Valery Pryamikov" <valery@harper.no> wrote in message
news:eLhL0qwXFHA.228@TK2MSFTNGP12.phx.gbl...
> myAssembly.GetName().GetPublicKey() returns you ASN1 DER encoded public
> key as
> RSAPublicKey ::= SEQUENCE {
> modulus INTEGER,
> publicExponent INTEGER
> }
> it means - it contain sequence's tag, size of the content, and big-endian
> integers for modulus and publicExponent. Modulus is prepended 0x0 byte for
> ensuring that leading bit will always be 0. Check your pk array to see
> binary presentation. snk file contains information recorded in different
> way that is proprietary and undocumented (except for code that comes with
> Rotor). Strongname.h only contains definition of PublicKeyBlob that
> consist of some extra information, but PublicKey inside of this structure
> is ASN1.DER encoded structure. For playing with public keys (and other ASN
> structures) you can use ASNDump utility (just Google for it).
> Arkady, I've told you about ASN1. from my first post to that thread. Can
> you, please, check the information I already gave you before asking any
> further questions...
>
> -Valery.
> http://www.harper.no/valery
>
>
> "Arkady Frenkel" <arkadyf@hotmailxdotx.com> wrote in message
> news:%23ejRPZiXFHA.3140@TK2MSFTNGP14.phx.gbl...
>> Let's continue:)..
>> I'll return to ASN.DER afterwards but now I want to dig into .NET format.
>> I did keypair file with sn.exe end extracted public key from it to file.
>> Now I can read it and make the hash of it with next :
>>
>> myAssemblyName.KeyPair = new StrongNameKeyPair(File.Open("KeyPair.snk",
>> FileMode.Open, FileAccess.Read));
>>
>> ...
>>
>> byte []pk;
>>
>> pk = myAssembly.GetName().GetPublicKey();
>>
>> SHA1Managed sha = new SHA1Managed() ;
>>
>> byte[] p = sha.ComputeHash(pk,0,pk.Length ) ;.
>>
>> byte []pt;
>>
>> pt = myAssembly.GetName().GetPublicKeyToken();
>>
>> And I see that reversed 8 last bytes of p[] are the same as
>> GetPublicKeyToken() return , so I see that all 160 bytes of Public key
>> .Net struct used for hash .
>>
>> I want to ask what is 3 dwords before PUBLICKEYSTRUCT ? The last from 3
>> is length ( 148 ) of BLOBHEADER(PUBLICKEYSTRUC)+RSAPUBKEY+
>> PUBLICKEYBLOB.
>> Are first and second are : ALG_ID & CALG_SHA1 ?They are 0x2400 &
>> 0x8004 in my case.
>>
>> TIA
>> Arkady
>>
>> "Arkady Frenkel" <arkadyf@hotmailxdotx.com> wrote in message
>> news:%23NVeFhHXFHA.3348@TK2MSFTNGP14.phx.gbl...
>>> Tnx Valery , I'm out of office and have take some to learn the stuff
>>> Arkady
>>>
>>> "Valery Pryamikov" <valery@harper.no> wrote in message
>>> news:OHiMnPGXFHA.3716@TK2MSFTNGP12.phx.gbl...
>>>> Well, that was the first time you actually revealed some of your
>>>> requirements :-).
>>>> in that case - you need to hash ASN1.DER encodded public key structure
>>>> as it is specified in PKCS#1. This is the same form of public key as
>>>> publickey blob stored inside X509 certificates and you can do it with
>>>> managed code only. In case if you can use interop to CAPI, or use .Net
>>>> 2.0. - it would spare you some low-level conversion work.
>>>> Check Mitch Gallant's web site for good description of ASN1 encoding
>>>> from .Net framework:
>>>> http://www.jensign.com/JavaScience/dotnet/JKeyNet/index.html
>>>>
>>>> For a sample aplication that uses a lot of C# to CAPI interop and does
>>>> lots of public key related processing you can check my old PPC
>>>> Certificate Manager sample:
>>>> http://www.gotdotnet.com/Community/UserSamples/Details.aspx?SampleGuid=68b9e2f2-7c36-417f-a218-e80557ae2957
>>>>
>>>> -Valery.
>>>> http://www.harper.no/valery
>>>>
>>>>
>>>> "Arkady Frenkel" <arkadyf@hotmailxdotx.com> wrote in message
>>>> news:e6l23zFXFHA.584@TK2MSFTNGP15.phx.gbl...
>>>>> No , I can't do it on my own .
>>>>> I need the way MSFT use it ( at least ) because I do it for UPnP
>>>>> device and other devices ( not mine obviously like PC can be UPnP
>>>>> device too , WiFi , cameras and so on ) receive that hashed value as
>>>>> identification ID due to UPnP security spec, so I can't do on my own
>>>>> but at least as MSFT do that and in managed code ( so can't use
>>>>> (C)API ).
>>>>>
>>>>> Arkady
>>>>>
>>>>> "Valery Pryamikov" <valery@harper.no> wrote in message
>>>>> news:ulQr0ZFXFHA.3712@TK2MSFTNGP09.phx.gbl...
>>>>>>I answered you several times you can hash your public key in many
>>>>>>different ways - all depends on your needs. Ex:
>>>>>> 1. Calculate hash on concatenation of little endian modulus with
>>>>>> little endian exponent without conversions (little endian is
>>>>>> presentation used by CAPI);
>>>>>> 2. Calculate hash on concatenation of little endian exponent with
>>>>>> little endian modulus without conversions;
>>>>>> 3. Calculate hash of little endian modulus and state that you are
>>>>>> expecting standard recommended public exponent only 0x1001 and fail
>>>>>> processing if exponent is different.
>>>>>> 4. Do as in 1, but convert both values to big endian;
>>>>>> 5. Do as in 2, but convert both values to big endian;
>>>>>> 6. Do as in 3, but convert modulus to big endian;
>>>>>> 7. Do as in 1, but convert both values to ASN1;
>>>>>> 8. Do as in 2, but convert both values to ASN1;
>>>>>> 9. Do as in 3, but convert modulus to ASN1;
>>>>>> 7. Do as in 1, but pack both values into xml format;
>>>>>> 8. Do as in 2, but pack both values into xml format;
>>>>>> 9. Do as in 3, but pack modulus into xml format;
>>>>>> 10. any variation of all above;
>>>>>> 11. Use CAPI's CryptExportKey and calculate hash on PLAINTEXTBLOB;
>>>>>> 12. Use CAPI's CryptExportKey and calculate hash on PUBLICKEYBLOB;
>>>>>> 13. Use CAPI's CryptEncodeObjectEx to pack public key into ASN1.DER
>>>>>> encoded structure of public key as specified in PKCS#1 and calculate
>>>>>> hash on that blob;
>>>>>> 14. In case if your public key is stored in certificate it is already
>>>>>> in the form as in 13 - retrieve public key blob and calculate hash on
>>>>>> that blob;
>>>>>>
>>>>>> I can add a hundred more practical suggestions on how to hash public
>>>>>> key. You didn't provide us with concrete requirements to make a
>>>>>> single practical suggestion. I have tried to explain that to you
>>>>>> several times. I did write that public key could be hashed in many
>>>>>> different ways depending on your requirements in several of my posts
>>>>>> to that thread.
>>>>>>
>>>>>> -Valery.
>>>>>> http://www.harper.no/valery
>>>>>>
>>>>>> "Arkady Frenkel" <arkadyf@hotmailxdotx.com> wrote in message
>>>>>> news:OZbLClEXFHA.1508@tk2msftngp13.phx.gbl...
>>>>>>>I ask very simple question and really want to read practical advice :
>>>>>>>how to calculate hash from public key , if you ( Valery ) want to
>>>>>>>think as I have to calculate public key token ( really I don't need
>>>>>>>that ) , but before to receive last 8 bytes ( token ) I have to
>>>>>>>receive all hash and that is my simple question. Do I need to send
>>>>>>>array of bytes of Modulus only or both ( Modulus and Exponent which
>>>>>>>is 3 ( that I wrote about ) in the case of RSA? I don't need theories
>>>>>>>of security algorithms and their output , just practical answer on
>>>>>>>my simple question.
>>>>>>> I have ( C# code ):
>>>>>>> RSACryptoServiceProvider rsa = new RSACryptoServiceProvider();
>>>>>>>
>>>>>>> RSAParameters rsaresult = new RSAParameters();
>>>>>>>
>>>>>>> rsaresult = rsa.ExportParameters(false);
>>>>>>>
>>>>>>> Now I have public key in the rsaresult and want to know if modulus
>>>>>>> will be enough for hash of public key , that's all I need . Like to
>>>>>>> extract token ( last reverced 8 bytes ) afterwards e.g.
>>>>>>>
>>>>>>> byte[] PKbytes = new byte [ rsaresult.Modulus.GetLength(0)/*
>>>>>>> probably or something else + rsaresult.Exponent.GetLength(0) */];
>>>>>>>
>>>>>>> rsaresult.Modulus.CopyTo(PKbytes,0);
>>>>>>>
>>>>>>> // probably or something else
>>>>>>>
>>>>>>> //
>>>>>>> rsaresult.Exponent.CopyTo(PKbytes,rsaresult.Modulus.GetLength(0));
>>>>>>>
>>>>>>> SHA1Managed sha = new SHA1Managed() ;
>>>>>>>
>>>>>>> byte[] b = sha.ComputeHash(PKbytes,0,PKbytes.Length ) ;
>>>>>>>
>>>>>>> All I want to know what have to be in PKbytes array to receive hash
>>>>>>> of
>>>>>>>
>>>>>>> public key.
>>>>>>>
>>>>>>> All I want practical answer on practical question ( please no theory
>>>>>>> , I have enough books around me )
>>>>>>>
>>>>>>> Arkady
>>>>>>>
>>>>>>> "Valery Pryamikov" <valery@harper.no> wrote in message
>>>>>>> news:eH09eNDXFHA.1044@TK2MSFTNGP10.phx.gbl...
>>>>>>>> "Arkady Frenkel" <arkadyf@hotmailxdotx.com> wrote in message
>>>>>>>> news:u9T$di%23WFHA.1796@TK2MSFTNGP15.phx.gbl...
>>>>>>>>> That not correct , exponent is 3 not 4 bytes. OTOH only 128 bytes
>>>>>>>>> used to calculate hash of public key not 131 and not 132.But both
>>>>>>>>> of you didn't answer my simple question what is algorithm of
>>>>>>>>> callculation hash from public key so I see I have to try other
>>>>>>>>> group, indirectly I see both in Windows and open source ( free
>>>>>>>>> ssl ) modulus used only but I'm not sure 100%
>>>>>>>>> Arkady
>>>>>>>>>
>>>>>>>> Hmm,
>>>>>>>> at first you are asking a completely meaningless question. We've
>>>>>>>> tried to clarify your requirements hoping that would show you the
>>>>>>>> answers that you were looking for. Instead you simply repeat your
>>>>>>>> meaningless question with extra mumbling about some number that you
>>>>>>>> taken from somewhere...
>>>>>>>> How to hash a public key? You take a hash function, send public key
>>>>>>>> as a parameter to a hash function and get the result. That's at
>>>>>>>> least how it is usually done.
>>>>>>>> And your "That not correct..." is in fact completely wrong.
>>>>>>>> Modulus and exponent are not measured in bytes, but in bits. You
>>>>>>>> are referring to 1024 bit modulus that becomes less and less used
>>>>>>>> due to simple fact that is providing less than 80 bits of security
>>>>>>>> (and just a couple of weeks ago 740 bits modulus 200 decimal digits
>>>>>>>> was successfully factored).
>>>>>>>> Public exponent could be any number from 3 up to large integer that
>>>>>>>> takes a half of bits of modulus (not bigger than that, since small
>>>>>>>> private exponents are vulnerable to Weiner's attack). The only
>>>>>>>> requirement for public and private exponents in rsa is that e*d=1
>>>>>>>> mod phi(m), where phi(m) is Euler's phi function and is
>>>>>>>> (p-1)*(q-1).
>>>>>>>> In fact, on other platforms than Windows it's quite usual to have
>>>>>>>> public exponent of the same size as private exponent and about
>>>>>>>> half-size of modulus, because in this case you actually can use
>>>>>>>> public key and private key interchangeably...
>>>>>>>>
>>>>>>>> But you know, what? I think that you were not really asking for
>>>>>>>> help....
>>>>>>>>
>>>>>>>> -Valery.
>>>>>>>> http://www.harper.no/valery
>>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>
>>>>>
>>>>>
>>>>
>>>
>>>
>>
>>
>
- Next message: Jakub Gwozdz: "WinLogon adds default certificate to "MY" store. Why, and how to disable?"
- Previous message: Valery Pryamikov: "Re: Hash of Public key"
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