Databases
StackOverflow2013
Postsdbo
PODecrypt a mesage using RSA in .NET - m**d mod p*q not working
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PODecrypt a mesage using RSA in .NET - m**d mod p*q not working
    primarykey
    data
    text
    <p>I am experimenting with Mega encryption API, and I am stuck with the RSA decryption part.</p> <p>The JavaScript used is this:</p> <pre><code>// Compute m**d mod p*q for RSA private key operations. function RSAdecrypt(m, d, p, q, u) { var xp = bmodexp(bmod(m,p), bmod(d,bsub(p,[1])), p); var xq = bmodexp(bmod(m,q), bmod(d,bsub(q,[1])), q); var t=bsub(xq,xp); if(t.length==0) { t=bsub(xp,xq); t=bmod(bmul(t, u), q); t=bsub(q,t); } else { t=bmod(bmul(t, u), q); } return badd(bmul(t,p), xp); } </code></pre> <p>I am using .NET (4.0 with support for BigInteger) and I am trying to replicate the same behaviour. </p> <p>The RSA data I have is:</p> <pre><code>p (1024 bits) q (1024 bits) d (2044 bits) u (1024 bits) m (2044 bits) (the ciphered data) </code></pre> <p>I tried with RSACryptoServiceProvider with no luck. In other <a href="https://stackoverflow.com/questions/14576424/how-do-i-use-rsacryptoserviceprovider-to-decrypt-given-that-i-only-have-p-q-d">post</a> another user reported that he managed using the basic RSA decryption algorithm (m**d mod p*q) and avoiding RSACryptoServiceProvider.</p> <p>I implemented it (the U part is not necessary, I understand), made sure that the input was exact the same as the Javascript input, but still had no luck. The ouput is not the same as the expected by the Javascript code.</p> <p>This is the function implemented:</p> <pre><code>Public Shared Function RSA_Decrypt(ByVal P As Numerics.BigInteger, ByVal Q As Numerics.BigInteger, ByVal D As Numerics.BigInteger, ByVal M As Numerics.BigInteger) As Byte() Dim N As System.Numerics.BigInteger = Numerics.BigInteger.Multiply(P, Q) Dim DecryptedData As System.Numerics.BigInteger = Numerics.BigInteger.ModPow(M, D, N) Return DecryptedData.ToByteArray End Function </code></pre> <p>The test code:</p> <pre><code>Dim P As New Numerics.BigInteger(Convert.FromBase64String("gbb1FjTy...s=")) Dim Q As New Numerics.BigInteger(Convert.FromBase64String("o0fGo0v...8=")) Dim D As New Numerics.BigInteger(Convert.FromBase64String("GFVe9C...bQ==")) Dim Data As New Numerics.BigInteger(Convert.FromBase64String("BnrSc/..Dg==")) Dim ResultBytes As Byte() = cripto.RSA_Decrypt(P, Q, D, Data) Dim ResultStr As String = Convert.ToBase64String(ResultBytes) </code></pre> <p>This code returns:</p> <pre><code>Vd2jBCzObTx...QW1y+VRSZHAw== </code></pre> <p>However, the JavaScript function returns </p> <pre><code>LUyj3pyIyr4g...1aZU= </code></pre> <p>Do you have an idea what am I doing wrong, and how I can solve this? </p>
    singulars
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. PTQuestion
    1. USCommunity
    1. USAndres_age
    plurals
    1. PL
      singulars
      1. LTLinked
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    1. VO
      singulars
      1. PODecrypt a mesage using RSA in .NET - m**d mod p*q not working
      1. This table or related slice is empty.
      1. VTDownMod
    1. COprobably an endianness issue. Guess your .net code uses little endian, and js uses big endian.
      singulars
      1. PODecrypt a mesage using RSA in .NET - m**d mod p*q not working
      1. USCodesInChaos
    2. COAnd using `ModPow` screams "timing-attack".
      singulars
      1. PODecrypt a mesage using RSA in .NET - m**d mod p*q not working
      1. USCodesInChaos
    3. COThanks for the comments, I never heard about "timing attack", will investigate... Regarding the big endian and little endian, I have tested it doing: `Convert.FromBase64String("...").Reverse.ToArray` And the result is still wrong :(
      singulars
      1. PODecrypt a mesage using RSA in .NET - m**d mod p*q not working
      1. USAndres_age
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload