How to extract exponents and modulus from SSH-RSA key files

Programmer Question

http://www.faqs.org/rfcs/rfc4253.html

::http://www.faqs.org/rfcs/rfc4251.html

Does anyone know the SSH key file format?

!! UPDATE

!! The base64 function I was using doesn't work. After running the key file through a different function (mozilla's built in atob()) the data fit into the specifications listed above.

I have rsa key files created with puttygen, but I must be missing something critical. Here is the hex of the public section:

00 00 00 07 73 73 68 2d 72 73 61 00 00 00 01 25
00 00 00 10 1c 1c 57 3f 4f 58 63 69 38 ad 19 35
b5 28 3d 78 53 35 53 6c 15 0e 69 23 ac 17 14 84
21 29 13 07 36 62 90 26 37 93 73 17 28 b8 ce 95
c3 11 24 21 61 b7 82 d9 04 42 97 f8 27 c3 44 06
46 ca e8 a3 a3 34 d7 3c c3 95 13 dd 16 1b 2c 29
7c 35 19 5f c2 7a 17 d5 14 0d 26 36 27 18 71 67
8d 9c 5b c4 7d 

first 4 bytes are UINT 7, the number of bytes inthe following string "ssh-rsa" but the format stops making sense after that. It SHOULD be followed by two MPINT but they lengths don't add up for the 3rd value.

Thanks!

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Using a numbered file descriptor from Java

Programmer Question

I need to access numbered file descriptors from Java -- other than 0, 1 or 2.

How can this be done? I looked at the FileDescriptor class but did'nt find any way to initialize it with a given file descriptor number.

As a concrete example lets suppose Java gets called as a child process from another programing language. File descriptors 3 and 4 are provided by the other language for input and output.

What I need in Java are InputStream and OutputStream objects connected to these file-descriptors, just like System.in, System.out and System.error are connected to file-desctiptors 0, 1 and 2.

I'm using Java 1.6 and this should run on Unix alike systems.

Tested working solution:

The answer with the file descriptor special filesystem entries did point me to the following workable solution:

1. find out if and where your Unix alike system has a special filesystem that contains named entries for all file descriptors.

   
   
   
   
   
   • I'm using FreeBSD where fdescfs(5) is a filesystem that does just this. Under Linux it would be procfs.
   
   



2. make sure this filesystem is mounted

   
   
   
   
   

   • FreeBSD: put fdescfs /dev/fd fdescfs rw 0 0 in /etc/fstab

     
     
     

     or run mount -t fdescfs null /dev/fd on a shell prompt (probably with sudo)

   
   



3. Use new FileInputStream("/dev/fd/3") and new FileOutputStream("/dev/fd/4") to get the streams connected to the filedescriptors (the paths are for FreeBSD, replace with your operating systems paths)

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Checking a null value in Objective-C that has been returned from a JSON string

Programmer Question

Heya,

I have a JSON object that is coming from a webserver.

The log is something like this:
{"status":"success","UserID":15,"Name":"John","DisplayName":"John","Surname":"Smith","Email":"email","Telephone":null,"FullAccount":"true"}

Note the Telephone is coming in as null if the user doesn't enter one.

When assigning this value to a NSString, in the NSLog it's coming out as

What is the correct way to check this value? It's preventing me from saving a NSDictionary.

I have tried using the conditions [myString length] and myString == nil and myString == NULL

Additionally where is the best place in the iOS documentation to read up on this?

Many thanks

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