When you execute
ssh-keygen -t ssh-dss
it generates two files: one containing the public and the other, the private key.
The ssh-keygen man-page says it always generates a 1024bit key, but when I open the public key file, I always get a 580 characters line (which would be
4640 bits in ASCII).
Am I missing something or thinking about it wrong? I've tried reading the algorithm, but it's very hard to calculate, considering the size of the prime numbers involved.
Is there a way I can validate if it's a 1024bit key from the quantity of characters in the id_dsa.pub file?
The files where ssh-keygen stores the public and private keys have some predefined format (PEM, ...), they are not a dump of the keys itself (remember, by example, that private key will be usually encrypted).
In this link (https://martin.kleppmann.com/2013/05/24/improving-security-of-ssh-private-keys.html) you will find some good explanations about the different formats, and usage of tools like "openssl asn1parse" to display them:
The private key is an ASN.1 data structure, serialized to a byte string using DER, and then Base64-encoded. ASN.1 is roughly comparable to JSON (it supports various data types such as integers, booleans, strings and lists/sequences that can be nested in a tree structure). It’s very widely used for cryptographic purposes, but it has somehow fallen out of fashion with the web generation (I don’t know why, it seems like a pretty decent format).
A method to find the public key size is look in the ASN1 for the tag that stores it and verify the length of its data.
Related
SAP servers are capable of encrypting and hashing data. But there doesn't appear to be a suitable API to call. SAP Note 1456433 talks about the class CL_SEC_SXML_XENCRYPTION. The signature of basic encryption is clearly geared towards SSF and unsuitable to basic private key encryption/decryption. I don't want/need envelopes and user certificates. Just private keys.
I found an AES library on GitHub AES library in ABAP and tweaked that to suit us. But it is very slow. I would like to use the encryption libraries SAP has. Clearly, the libraries are there but find a suitably exposed API seems the issue.
Does anybody know how to use basic encryption in SAP?
In SAP ABAP stack, using ABAP.
Eg (a call to use AES-CBC 128, with PKCS7 padding
where only a private key and data to encrypt is required. As example:
public static method encrypt_xstring
importing i_key type xstring
i_data type xstring
i_initialization_vector type xstring optional
i_padding_standard type char10 optional
i_encryption_mode type char10 optional
exporting e_data type xstring
Use case is encrypting data on clients with a private key and sending the data to SAP system. The source supports private keys and libraries like AES-CBC.
And we have encrypted data interchange working.
Next step is to use a supported and faster library.
EDIT: In case anyone needs to encryption / decryption properly in abap
And is looking at the answer. Use class CL_SEC_SXML_WRITER.
CL_SEC_SXML_WRITER was exactly what i was looking for
BUT SAP didnt expose it properly. It is only useful for encryption no decryption.
When interacting with external libraries. Where PKCS7 padding is used and SALTs
or Initialization vectors are required.
SAP offer an ENCRYPT_IV but no Decrypt_IV. Why ????
So you cant use the tool and remain compliant. :(
It is not considered safe to use AES-CBC without IV.
Why would SAP do that ?
ENCRYPT_IV instead of ENCRYPT but no DECRYPT_IV
The offer an Add Padding but no remove padding. OK roll your own padding removal, no big deal. Its like the must be another library for the other direction.
So i can use the tool to encrypt but not decrypt.
My main problem was decrypting quickly strings sent from a mobile device.
So still need to use the old ABAP code for that :(
I have similar requirements and I found the cl_sec_sxml_writer class. Please have a look at the following example. Note that the writer requires XSTRING parameters which is why I'm using conversion classes.
REPORT zged_aes.
DATA lv_message_string TYPE string.
" create message
DATA(lr_conv_sec) = cl_abap_conv_out_ce=>create( ).
lr_conv_sec->write( data = 'This is my secret' ).
" create key
DATA(lr_conv_key) = cl_abap_conv_out_ce=>create( ).
lr_conv_key->write( data = 'MySymmetricKey' ).
" encrypt using AES256
cl_sec_sxml_writer=>encrypt(
EXPORTING
plaintext = lr_conv_sec->get_buffer( )
key = lr_conv_key->get_buffer( )
algorithm = cl_sec_sxml_writer=>co_aes256_algorithm_pem
IMPORTING
ciphertext = DATA(lv_message) ).
" decrypt message
cl_sec_sxml_writer=>decrypt(
EXPORTING
ciphertext = lv_message
key = lr_conv_key->get_buffer( )
algorithm = cl_sec_sxml_writer=>co_aes256_algorithm_pem
IMPORTING
plaintext = DATA(lv_message_decrypted) ).
" convert xstring to string for output
cl_abap_conv_in_ce=>create( input = lv_message_decrypted)->read( IMPORTING data = lv_message_string ).
" output secret message
WRITE lv_message_string.
I tested it on a NetWeaver 7.50 SP 6 system.
I got the ENCRYPT_IV method to work alongside method DECRYPT of class CL_SEC_SXML_WRITER.
The caveat here is that I didn't generate the Symmetric Key and IV by making use of Class cl_abap_conv_out_ce.
I already had my keys and IV from a Java implementation test.
The only thing I needed was to create the Key and IV as an XSTRING and initializing them with the Hex format of my Java implementation (they were in Byte format.
Because of this, I first converted them to Hex and passed those values to the ABAP Xstring types).
The code encrypt/decrypt function with openssl library, like following...
EVP_EncryptInit_ex( ctx, EVP_aes_256_cbc(), NULL, key, iv)
It can work, when the key length is not equal 256 bits(32 bytes).
The key length can be any. Why?
For example, it works fine, and no error received:
char key[]="012345678901234567890";
Why does EVP_CIPHER is EVP_aes_256_cbc() succeed when key length is not equal 256bits?
You seem to be asking why you can encrypt using EVP_aes_256_cbc when the key is smaller, like 128-bits.
If you supply an undersized key you are reading random bytes/garbage at the tail of the key bytes. The function is reading bytes, but you don't know what they are. You may get lucky on the local machine and be able to encrypt and decrypt. It will almost certainly fail to decrypt on a different machine.
Valgrind should alert you to the problem of reading uninaitalezed [key] memory. Asan should alert about a read in a guard zone.
I don't believe EVP_aes_256_cbc pads or expands. Like #Zaph said, always use the correct size. If you need to "stretch" a smaller key into a bigger one, then see HMAC-based Extract-and-Expand Key Derivation Function (HKDF), which extracts entropy then expands it.
I am using 128-bit Rijndael with ECB cipher mode encryption to convert my string. It formats some kind of string with symbols == or = at the end.
In my code I need some preliminary decision was this string encrypted. Can I suggest that if it contains = symbol at the end it is encrypted or possible cases when I will not get = symbol in the end in encrypted string?
First of all, if you are using ECB you are not really "encrypting" since it is a broken cipher mode (see: http://bobnalice.wordpress.com/2009/01/28/friends-don%E2%80%99t-let-friends-use-ecb-mode-encryption/ )
Secondly, the = signs you are seeing are the Base64 padding characters. They are only tagentially related to encryption since Base64 is used for any kind of binary data, not just encrypted date.
Thirdly, you can't even rely on the = sign always being present for Base64 data... it is only added for certain lengths of data (i.e. you could have encrypted, Base64 data that has no = sign)
As #JoelFan points out, those '=' characters are Base64 padding which aren't part of the encryption at all, and aren't always there either if the data comes out to the right number of characters naturally.
You need to add something "out of band". I would replace the potentially-encrypted string with a class which has a string member for the data, and an "encrypted" flag. Once you're there, throw in a getData() method that checks if the instance's data is encrypted, returns the unencrypted value of the data if so (and may cache the plaintext in a private member for later, if it'll be accessed a lot), or just returns the plain text if it's not encrypted.
I need a piece of code that defines functions which can encrypt and decrypt a piece of string. What I basically want is that the string should not be visible to third-party users, so that when the string originates in one file, it is converted to, say, an integer value using the encrypt function and then it is passed as parameter to another file. There the decrpyt function then decrypts it back and uses the string to perform actions on it.
Any suggestions or already available codes will be just fine!
Please help me out. Thanks!
Install tcllib. There are several standard encryption algorithms implemented in tcllib.
The following encryption algorithms are available:
blowfish: http://tcllib.sourceforge.net/doc/blowfish.html
aes: http://tcllib.sourceforge.net/doc/aes.html
des (including triple des): http://tcllib.sourceforge.net/doc/des.html
rc4: http://tcllib.sourceforge.net/doc/rc4.html
The des package in Tcllib should do what you want. It's pretty easy to use:
package require des
set key "12345678"; # Must be 8 bytes long
set msg "abcde"
##### ENCRYPTION
set encryptedMsg [DES::des -dir encrypt -key $key $msg]
# $encryptedMsg is a bunch of bytes; you'll want to send this around...
##### DECRYPTION
set decryptedMsg [DES::des -dir decrypt -key $key $encryptedMsg]
puts "I got '$decryptedMsg'"
Note that DES will pad the message out to a multiple of 8 bytes long.
Please visit the TCL/TK homepage e.g
here:http://wiki.tcl.tk/900
That's just one way of doing it. There will be much more, I'm sure.
I run a rather large site where my members add thousands of images every day. Obviously there is a lot of duplication and i was just wondering if during an upload of an image i can somehow generate a signature or a hash of an image so i can store it. And every time someone uploads the picture i would simply run a check if this signature already exists and fire an error stating that this image already exists. Not sure if this kind of technology already exists for asp.net but i am aware of tineye.com which sort of does it already.
If you think you can help i would appreciate your input.
Kris
A keyword that might be of interest is perceptual hashing.
You use any derived HashAlgorithm to generate a hash from the byte array of the file. Usually MD5 is used, but you could subsitute this for any of those provided in the System.Security.Cryptography namespace. This works for any binary, not just images.
Lots of sites provide MD5 hashes when you download files to verify if you've downloaded the file properly. For instance, an ISO CD/DVD image may be missing bytes when you've received the whole thing. Once you've downloaded the file, you generate the hash for it and make sure it's the same as the site says it should be. If all compares, you've got an exact copy.
I would probably use something similar to this:
public static class Helpers
{
//If you're running .NET 2.0 or lower, remove the 'this' keyword from the
//method signature as 2.0 doesn't support extension methods.
static string GetHashString(this byte[] bytes, HashAlgorithm cryptoProvider)
{
byte[] hash = cryptoProvider.ComputeHash(bytes);
return Convert.ToBase64String(hash);
}
}
Requires:
using System.Security.Cryptography;
Call using:
byte[] bytes = File.ReadAllBytes("FilePath");
string filehash = bytes.GetHashString(new MD5CryptoServiceProvider());
or if you're running in .NET 2.0 or lower:
string filehash = Helpers.GetHashString(File.ReadAllBytes("FilePath"), new MD5CryptoServiceProvider());
If you were to decide to go with a different hashing method instead of MD5 for the miniscule probability of collisions:
string filehash = bytes.GetHashString(new SHA1CryptoServiceProvider());
This way your has method isn't crypto provider specific and if you were to decide you wanted to change which crypto provider you're using, you just inject a different one into the cryptoProvider parameter.
You can use any of the other hashing classes just by changing the service provider you pass in:
string md5Hash = bytes.GetHashString(new MD5CryptoServiceProvider());
string sha1Hash = bytes.GetHashString(new SHA1CryptoServiceProvider());
string sha256Hash = bytes.GetHashString(new SHA256CryptoServiceProvider());
string sha384Hash = bytes.GetHashString(new SHA384CryptoServiceProvider());
string sha512Hash = bytes.GetHashString(new SHA512CryptoServiceProvider());
Typically you'd just use MD5 or similar to create a hash. This isn't guaranteed to be unique though, so I'd recommend you use the hash as a starting point. Identify if the image matches any known hashes you stored, then individually load the ones that it does match and do a full byte comparison on the potential collisions to be sure.
Another, simpler technique though is to simply pick a smallish number of bits and read first part of the image... store that number of starting bits as if they were a hash. This still gives you a small number of potential collisions that you'd need to check, but has much less overhead.
Look in the System.Security.Cryptography namespace. You have your choice of several hashing algorithms/implementations. Here's an example using md5, but since you have a lot of these you might want something bigger like SHA1:
public byte[] HashImage(Stream imageData)
{
return new MD5CryptoServiceProvider().ComputeHash(imageData);
}
I don't know if it already exists or not, but I can't think of a reason you can't do this yourself. Something similar to this will get you a hash of the file.
var fileStream = Request.Files[0].InputStream;//the uploaded file
var hasher = System.Security.Cryptography.HMACMD5();
var theHash = hasher.ComputeHash(fileStream);
System.Security.Cryptography