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  • Can hash tables really be O(1)

    - by drawnonward
    It seems to be common knowledge that hash tables can achieve O(1) but that has never made sense to me. Can someone please explain it? A. The value is an int smaller than the size of the hash table, so the value is its own hash, so there is no hash table but if there was it would be O(1) and still be inefficient. B. You have to calculate the hash, so the order is O(n) for the size of the data being looked up. The lookup might be O(1) after you do O(n) work, but that still comes out to O(n) in my eyes. And unless you have a perfect hash or a large hash table there are probably several items per bucket so it devolves into a small linear search at some point anyway. I think hash tables are awesome, but I do not get the O(1) designation unless it is just supposed to be theoretical.

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  • C++0x, How do I expand a tuple into variadic template function arguments?

    - by Gustaf
    Consider the case of a templated function with variadic template arguments: template<typename Tret, typename... T> Tret func(const T&... t); Now, I have a tuple t of values. How do I call func() using the tuple values as arguments? I've read about the bind() function object, with call() function, and also the apply() function in different some now-obsolete documents. The GNU GCC 4.4 implementation seems to have a call() function in the bind() class, but there is very little documentation on the subject. Some people suggest hand-written recursive hacks, but the true value of variadic template arguments is to be able to use them in cases like above. Does anyone have a solution to is, or hint on where to read about it?

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  • Hash Algorithm Randomness Visualization

    - by clstroud
    I'm curious if anyone here has any idea how the images were generated as shown in this response: Which hashing algorithm is best for uniqueness and speed? Ian posted a very well-received response but I can't seem to understand how he went about making the images. I hate to make a new question dedicated to this, but I can't find any means to ask him more directly. On the other hand, perhaps someone has an alternative perspective. The best I can personally come up with would be to have it almost like a bar graph, which would illustrate how evenly the buckets of the hash table are being generated. I have a working Cocoa program that does this, but it can't generate anything like what he showed there. So the question is two fold I suppose: A) How does one truly interpret the data he shows? Is it more than "less whitespace = better"? B) How does one generate such an image based on some set of inputs, a hash, and an index? Perhaps I'm misunderstanding entirely, but I really would like to know more about this particular visualization technique. Or maybe I'm mis-applying this to hash tables rather than just hashes in general, but in that case I don't know how it would be "bounded" for the image.

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  • What is New in ASP.NET 4.0 Code Access Security

    - by Xiaohong
    ASP.NET Code Access Security (CAS) is a feature that helps protect server applications on hosting multiple Web sites, ASP.NET lets you assign a configurable trust level that corresponds to a predefined set of permissions. ASP.NET has predefined ASP.NET Trust Levels and Policy Files that you can assign to applications, you also can assign custom trust level and policy files. Most web hosting companies run ASP.NET applications in Medium Trust to prevent that one website affect or harm another site etc. As .NET Framework's Code Access Security model has evolved, ASP.NET 4.0 Code Access Security also has introduced several changes and improvements. The main change in ASP.NET 4.0 CAS In ASP.NET v4.0 partial trust applications, application domain can have a default partial trust permission set as opposed to being full-trust, the permission set name is defined in the <trust /> new attribute permissionSetName that is used to initialize the application domain . By default, the PermissionSetName attribute value is "ASP.Net" which is the name of the permission set you can find in all predefined partial trust configuration files. <trust level="Something" permissionSetName="ASP.Net" /> This is ASP.NET 4.0 new CAS model. For compatibility ASP.NET 4.0 also support legacy CAS model where application domain still has full trust permission set. You can specify new legacyCasModel attribute on the <trust /> element to indicate whether the legacy CAS model is enabled. By default legacyCasModel is false which means that new 4.0 CAS model is the default. <trust level="Something" legacyCasModel="true|false" /> In .Net FX 4.0 Config directory, there are two set of predefined partial trust config files for each new CAS model and legacy CAS model, trust config files with name legacy.XYZ.config are for legacy CAS model: New CAS model: Legacy CAS model: web_hightrust.config legacy.web_hightrust.config web_mediumtrust.config legacy.web_mediumtrust.config web_lowtrust.config legacy.web_lowtrust.config web_minimaltrust.config legacy.web_minimaltrust.config   The figure below shows in ASP.NET 4.0 new CAS model what permission set to grant to code for partial trust application using predefined partial trust levels and policy files:    There also some benefits that comes with the new CAS model: You can lock down a machine by making all managed code no-execute by default (e.g. setting the MyComputer zone to have no managed execution code permissions), it should still be possible to configure ASP.NET web applications to run as either full-trust or partial trust. UNC share doesn’t require full trust with CASPOL at machine-level CAS policy. Side effect that comes with the new CAS model: processRequestInApplicationTrust attribute is deprecated  in new CAS model since application domain always has partial trust permission set in new CAS model.   In ASP.NET 4.0 legacy CAS model or ASP.NET 2.0 CAS model, even though you assign partial trust level to a application but the application domain still has full trust permission set. The figure below shows in ASP.NET 4.0 legacy CAS model (or ASP.NET 2.0 CAS model) what permission set to grant to code for partial trust application using predefined partial trust levels and policy files:     What $AppDirUrl$, $CodeGen$, $Gac$ represents: $AppDirUrl$ The application's virtual root directory. This allows permissions to be applied to code that is located in the application's bin directory. For example, if a virtual directory is mapped to C:\YourWebApp, then $AppDirUrl$ would equate to C:\YourWebApp. $CodeGen$ The directory that contains dynamically generated assemblies (for example, the result of .aspx page compiles). This can be configured on a per application basis and defaults to %windir%\Microsoft.NET\Framework\{version}\Temporary ASP.NET Files. $CodeGen$ allows permissions to be applied to dynamically generated assemblies. $Gac$ Any assembly that is installed in the computer's global assembly cache (GAC). This allows permissions to be granted to strong named assemblies loaded from the GAC by the Web application.   The new customization of CAS Policy in ASP.NET 4.0 new CAS model 1. Define which named permission set in partial trust configuration files By default the permission set that will be assigned at application domain initialization time is the named "ASP.Net" permission set found in all predefined partial trust configuration files. However ASP.NET 4.0 allows you set PermissionSetName attribute to define which named permission set in a partial trust configuration file should be the one used to initialize an application domain. Example: add "ASP.Net_2" named permission set in partial trust configuration file: <PermissionSet class="NamedPermissionSet" version="1" Name="ASP.Net_2"> <IPermission class="FileIOPermission" version="1" Read="$AppDir$" PathDiscovery="$AppDir$" /> <IPermission class="ReflectionPermission" version="1" Flags ="RestrictedMemberAccess" /> <IPermission class="SecurityPermission " version="1" Flags ="Execution, ControlThread, ControlPrincipal, RemotingConfiguration" /></PermissionSet> Then you can use "ASP.Net_2" named permission set for the application domain permission set: <trust level="Something" legacyCasModel="false" permissionSetName="ASP.Net_2" /> 2. Define a custom set of Full Trust Assemblies for an application By using the new fullTrustAssemblies element to configure a set of Full Trust Assemblies for an application, you can modify set of partial trust assemblies to full trust at the machine, site or application level. The configuration definition is shown below: <fullTrustAssemblies> <add assemblyName="MyAssembly" version="1.1.2.3" publicKey="hex_char_representation_of_key_blob" /></fullTrustAssemblies> 3. Define <CodeGroup /> policy in partial trust configuration files ASP.NET 4.0 new CAS model will retain the ability for developers to optionally define <CodeGroup />with membership conditions and assigned permission sets. The specific restriction in ASP.NET 4.0 new CAS model though will be that the results of evaluating custom policies can only result in one of two outcomes: either an assembly is granted full trust, or an assembly is granted the partial trust permission set currently associated with the running application domain. It will not be possible to use custom policies to create additional custom partial trust permission sets. When parsing the partial trust configuration file: Any assemblies that match to code groups associated with "PermissionSet='FullTrust'" will run at full trust. Any assemblies that match to code groups associated with "PermissionSet='Nothing'" will result in a PolicyError being thrown from the CLR. This is acceptable since it provides administrators with a way to do a blanket-deny of managed code followed by selectively defining policy in a <CodeGroup /> that re-adds assemblies that would be allowed to run. Any assemblies that match to code groups associated with other permissions sets will be interpreted to mean the assembly should run at the permission set of the appdomain. This means that even though syntactically a developer could define additional "flavors" of partial trust in an ASP.NET partial trust configuration file, those "flavors" will always be ignored. Example: defines full trust in <CodeGroup /> for my strong named assemblies in partial trust config files: <CodeGroup class="FirstMatchCodeGroup" version="1" PermissionSetName="Nothing"> <IMembershipCondition    class="AllMembershipCondition"    version="1" /> <CodeGroup    class="UnionCodeGroup"    version="1"    PermissionSetName="FullTrust"    Name="My_Strong_Name"    Description="This code group grants code signed full trust. "> <IMembershipCondition      class="StrongNameMembershipCondition" version="1"       PublicKeyBlob="hex_char_representation_of_key_blob" /> </CodeGroup> <CodeGroup   class="UnionCodeGroup" version="1" PermissionSetName="ASP.Net">   <IMembershipCondition class="UrlMembershipCondition" version="1" Url="$AppDirUrl$/*" /> </CodeGroup> <CodeGroup class="UnionCodeGroup" version="1" PermissionSetName="ASP.Net">   <IMembershipCondition class="UrlMembershipCondition" version="1" Url="$CodeGen$/*"   /> </CodeGroup></CodeGroup>   4. Customize CAS policy at runtime in ASP.NET 4.0 new CAS model ASP.NET 4.0 new CAS model allows to customize CAS policy at runtime by using custom HostSecurityPolicyResolver that overrides the ASP.NET code access security policy. Example: use custom host security policy resolver to resolve partial trust web application bin folder MyTrustedAssembly.dll to full trust at runtime: You can create a custom host security policy resolver and compile it to assembly MyCustomResolver.dll with strong name enabled and deploy in GAC: public class MyCustomResolver : HostSecurityPolicyResolver{ public override HostSecurityPolicyResults ResolvePolicy(Evidence evidence) { IEnumerator hostEvidence = evidence.GetHostEnumerator(); while (hostEvidence.MoveNext()) { object hostEvidenceObject = hostEvidence.Current; if (hostEvidenceObject is System.Security.Policy.Url) { string assemblyName = hostEvidenceObject.ToString(); if (assemblyName.Contains(“MyTrustedAssembly.dll”) return HostSecurityPolicyResult.FullTrust; } } //default fall-through return HostSecurityPolicyResult.DefaultPolicy; }} Because ASP.NET accesses the custom HostSecurityPolicyResolver during application domain initialization, and a custom policy resolver requires full trust, you also can add a custom policy resolver in <fullTrustAssemblies /> , or deploy in the GAC. You also need configure a custom HostSecurityPolicyResolver instance by adding the HostSecurityPolicyResolverType attribute in the <trust /> element: <trust level="Something" legacyCasModel="false" hostSecurityPolicyResolverType="MyCustomResolver, MyCustomResolver" permissionSetName="ASP.Net" />   Note: If an assembly policy define in <CodeGroup/> and also in hostSecurityPolicyResolverType, hostSecurityPolicyResolverType will win. If an assembly added in <fullTrustAssemblies/> then the assembly has full trust no matter what policy in <CodeGroup/> or in hostSecurityPolicyResolverType.   Other changes in ASP.NET 4.0 CAS Use the new transparency model introduced in .Net Framework 4.0 Change in dynamically compiled code generated assemblies by ASP.NET: In new CAS model they will be marked as security transparent level2 to use Framework 4.0 security transparent rule that means partial trust code is treated as completely Transparent and it is more strict enforcement. In legacy CAS model they will be marked as security transparent level1 to use Framework 2.0 security transparent rule for compatibility. Most of ASP.NET products runtime assemblies are also changed to be marked as security transparent level2 to switch to SecurityTransparent code by default unless SecurityCritical or SecuritySafeCritical attribute specified. You also can look at Security Changes in the .NET Framework 4 for more information about these security attributes. Support conditional APTCA If an assembly is marked with the Conditional APTCA attribute to allow partially trusted callers, and if you want to make the assembly both visible and accessible to partial-trust code in your web application, you must add a reference to the assembly in the partialTrustVisibleAssemblies section: <partialTrustVisibleAssemblies> <add assemblyName="MyAssembly" publicKey="hex_char_representation_of_key_blob" />/partialTrustVisibleAssemblies>   Most of ASP.NET products runtime assemblies are also changed to be marked as conditional APTCA to prevent use of ASP.NET APIs in partial trust environments such as Winforms or WPF UI controls hosted in Internet Explorer.   Differences between ASP.NET new CAS model and legacy CAS model: Here list some differences between ASP.NET new CAS model and legacy CAS model ASP.NET 4.0 legacy CAS model  : Asp.net partial trust appdomains have full trust permission Multiple different permission sets in a single appdomain are allowed in ASP.NET partial trust configuration files Code groups Machine CAS policy is honored processRequestInApplicationTrust attribute is still honored    New configuration setting for legacy model: <trust level="Something" legacyCASModel="true" ></trust><partialTrustVisibleAssemblies> <add assemblyName="MyAssembly" publicKey="hex_char_representation_of_key_blob" /></partialTrustVisibleAssemblies>   ASP.NET 4.0 new CAS model: ASP.NET will now run in homogeneous application domains. Only full trust or the app-domain's partial trust grant set, are allowable permission sets. It is no longer possible to define arbitrary permission sets that get assigned to different assemblies. If an application currently depends on fine-tuning the partial trust permission set using the ASP.NET partial trust configuration file, this will no longer be possible. processRequestInApplicationTrust attribute is deprecated Dynamically compiled assemblies output by ASP.NET build providers will be updated to explicitly mark assemblies as transparent. ASP.NET partial trust grant sets will be independent from any enterprise, machine, or user CAS policy levels. A simplified model for locking down web servers that only allows trusted managed web applications to run. Machine policy used to always grant full-trust to managed code (based on membership conditions) can instead be configured using the new ASP.NET 4.0 full-trust assembly configuration section. The full-trust assembly configuration section requires explicitly listing each assembly as opposed to using membership conditions. Alternatively, the membership condition(s) used in machine policy can instead be re-defined in a <CodeGroup /> within ASP.NET's partial trust configuration file to grant full-trust.   New configuration setting for new model: <trust level="Something" legacyCASModel="false" permissionSetName="ASP.Net" hostSecurityPolicyResolverType=".NET type string" ></trust><fullTrustAssemblies> <add assemblyName=”MyAssembly” version=”1.0.0.0” publicKey="hex_char_representation_of_key_blob" /></fullTrustAssemblies><partialTrustVisibleAssemblies> <add assemblyName="MyAssembly" publicKey="hex_char_representation_of_key_blob" /></partialTrustVisibleAssemblies>     Hope this post is helpful to better understand the ASP.Net 4.0 CAS. Xiaohong Tang ASP.NET QA Team

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  • Partial Rendering with Update Progress Bar Using AJAX and jQuery

    This article guides about showing an update progress bar while partial page rendering. It also covers about writing data in XML file as well....Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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  • Partial rendering control using JQuery in MVC 2

    This article show a web custom control that allows partial rendering using JQuery in a MVC 2 web application...Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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  • Efficient, partial, point-in-time database restores

    - by GavinPayneUK
    This article is about a situation that many of us could describe the theoretical approach to solving, but then struggle to understand why SQL Server wasn’t following that theoretical approach when you tried it for real. Earlier this week, I had a client ask about the best way to perform: a partial database restore, 1 of 1300 filegroups; to a specific point in time; using a differential backup, and therefore; without restoring each transaction log backup taken since the full backup. The last point...(read more)

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  • ASP.NET Web Form Model with Partial Rendering and Events

    This article explains the Event based ASP.NET Web Form programming model for a web application with reference to partial rendering and AJAX asynchronous postback....Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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  • Partial rendering control using JQuery

    This article show a web custom control that allows partial rendering using JQuery...Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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  • Should strongly typed partial views on one page in asp.net mvc-2 have one combined view model?

    - by Kai
    Hi guys, I have a question about asp.net mvc-2 strongly typed partial views, and view models. I was just wondering if I can (or should) have two strongly typed partial views on one page, without implementing a whole new view model for that page. For example, I have a page that displays profiles, but also has an inline form to add a quick contact. Each of these entities already has it's own view model, i.e I have a ProfileViewModel and a ContactViewModel. So my view needs two strongly typed partial views, one using an IEnumerable List of ProfileViewModels, and one using a ContactViewModel. Is it possible or desirable to avoid making a third view model, an 'IndexViewModel' for this page, which holds a list of ProfileViewModels and a ContactViewModel? Is not implementing this view model bad practice, or tidier as it results in less view models? Thanks!

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  • grep - what arguments do you usually specify?

    - by meder
    My most common grep line is just.. grep -IRl "text" * However I'm kinda getting tired of retyping this over and over - is there some way I can make an alias command so that those arguments are always enabled? And, I was wondering what arguments you usually specify for text searching - my two arguments 'R' for recursion, 'I' for not including binary types like jpg/gif, and 'l' for line number seem a bit too minimal. Which arguments do you use?

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  • Why doesn't functools.partial return a real function (and how to create one that does)?

    - by epsilon
    So I was playing around with currying functions in Python and one of the things that I noticed was that functools.partial returns a partial object rather than an actual function. One of the things that annoyed me about this was that if I did something along the lines of: five = partial(len, 'hello') five('something') then we get TypeError: len() takes exactly 1 argument (2 given) but what I want to happen is TypeError: five() takes no arguments (1 given) Is there a clean way to make it work like this? I wrote a workaround, but it's too hacky for my taste (doesn't work yet for functions with varargs): def mypartial(f, *args): argcount = f.func_code.co_argcount - len(args) params = ''.join('a' + str(i) + ',' for i in xrange(argcount)) code = ''' def func(f, args): def %s(%s): return f(*(args+(%s))) return %s ''' % (f.func_name, params, params, f.func_name) exec code in locals() return func(f, args)

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  • Get a list/tuple/dict of the arguments passed to a function?

    - by digitala
    Given the following function: def foo(a, b, c): pass How would one obtain a list/tuple/dict/etc of the arguments passed in, without having to build the structure myself? Specifically, I'm looking for Python's version of JavaScript's arguments keyword or PHP's func_get_args() method. What I'm not looking for is a solution using *args or **kwargs; I need to specify the argument names in the function definition (to ensure they're being passed in) but within the function I want to work with them in a list- or dict-style structure.

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  • Get a list/tuple/dict of *all* the arguments passed to a function?

    - by Phillip Oldham
    Given the following function: def foo(a, b, c): pass How would one obtain a list/tuple/dict/etc of the arguments passed in? Specifically, I'm looking for Python's version of JavaScript's arguments keyword or PHP's func_get_args() method. What I'm not looking for is a solution using *args or **kwargs; I need to specify the argument names in the function definition (to ensure they're being passed in) but within the function I want to work with them in a list- or dict-style structure.

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  • How can * be a safe hashed password?

    - by Exception e
    phpass is a widely used hashing 'framework'. While evaluating phpass' HashPassword I came across this odd method fragment. function HashPassword($password) { // <snip> trying to generate a hash… # Returning '*' on error is safe here, but would _not_ be safe # in a crypt(3)-like function used _both_ for generating new # hashes and for validating passwords against existing hashes. return '*'; } This is the complete phpsalt class: # Portable PHP password hashing framework. # # Version 0.2 / genuine. # # Written by Solar Designer <solar at openwall.com> in 2004-2006 and placed in # the public domain. # # # class PasswordHash { var $itoa64; var $iteration_count_log2; var $portable_hashes; var $random_state; function PasswordHash($iteration_count_log2, $portable_hashes) { $this->itoa64 = './0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz'; if ($iteration_count_log2 < 4 || $iteration_count_log2 > 31) $iteration_count_log2 = 8; $this->iteration_count_log2 = $iteration_count_log2; $this->portable_hashes = $portable_hashes; $this->random_state = microtime() . getmypid(); } function get_random_bytes($count) { $output = ''; if (is_readable('/dev/urandom') && ($fh = @fopen('/dev/urandom', 'rb'))) { $output = fread($fh, $count); fclose($fh); } if (strlen($output) < $count) { $output = ''; for ($i = 0; $i < $count; $i += 16) { $this->random_state = md5(microtime() . $this->random_state); $output .= pack('H*', md5($this->random_state)); } $output = substr($output, 0, $count); } return $output; } function encode64($input, $count) { $output = ''; $i = 0; do { $value = ord($input[$i++]); $output .= $this->itoa64[$value & 0x3f]; if ($i < $count) $value |= ord($input[$i]) << 8; $output .= $this->itoa64[($value >> 6) & 0x3f]; if ($i++ >= $count) break; if ($i < $count) $value |= ord($input[$i]) << 16; $output .= $this->itoa64[($value >> 12) & 0x3f]; if ($i++ >= $count) break; $output .= $this->itoa64[($value >> 18) & 0x3f]; } while ($i < $count); return $output; } function gensalt_private($input) { $output = '$P$'; $output .= $this->itoa64[min($this->iteration_count_log2 + ((PHP_VERSION >= '5') ? 5 : 3), 30)]; $output .= $this->encode64($input, 6); return $output; } function crypt_private($password, $setting) { $output = '*0'; if (substr($setting, 0, 2) == $output) $output = '*1'; if (substr($setting, 0, 3) != '$P$') return $output; $count_log2 = strpos($this->itoa64, $setting[3]); if ($count_log2 < 7 || $count_log2 > 30) return $output; $count = 1 << $count_log2; $salt = substr($setting, 4, 8); if (strlen($salt) != 8) return $output; # We're kind of forced to use MD5 here since it's the only # cryptographic primitive available in all versions of PHP # currently in use. To implement our own low-level crypto # in PHP would result in much worse performance and # consequently in lower iteration counts and hashes that are # quicker to crack (by non-PHP code). if (PHP_VERSION >= '5') { $hash = md5($salt . $password, TRUE); do { $hash = md5($hash . $password, TRUE); } while (--$count); } else { $hash = pack('H*', md5($salt . $password)); do { $hash = pack('H*', md5($hash . $password)); } while (--$count); } $output = substr($setting, 0, 12); $output .= $this->encode64($hash, 16); return $output; } function gensalt_extended($input) { $count_log2 = min($this->iteration_count_log2 + 8, 24); # This should be odd to not reveal weak DES keys, and the # maximum valid value is (2**24 - 1) which is odd anyway. $count = (1 << $count_log2) - 1; $output = '_'; $output .= $this->itoa64[$count & 0x3f]; $output .= $this->itoa64[($count >> 6) & 0x3f]; $output .= $this->itoa64[($count >> 12) & 0x3f]; $output .= $this->itoa64[($count >> 18) & 0x3f]; $output .= $this->encode64($input, 3); return $output; } function gensalt_blowfish($input) { # This one needs to use a different order of characters and a # different encoding scheme from the one in encode64() above. # We care because the last character in our encoded string will # only represent 2 bits. While two known implementations of # bcrypt will happily accept and correct a salt string which # has the 4 unused bits set to non-zero, we do not want to take # chances and we also do not want to waste an additional byte # of entropy. $itoa64 = './ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789'; $output = '$2a$'; $output .= chr(ord('0') + $this->iteration_count_log2 / 10); $output .= chr(ord('0') + $this->iteration_count_log2 % 10); $output .= '$'; $i = 0; do { $c1 = ord($input[$i++]); $output .= $itoa64[$c1 >> 2]; $c1 = ($c1 & 0x03) << 4; if ($i >= 16) { $output .= $itoa64[$c1]; break; } $c2 = ord($input[$i++]); $c1 |= $c2 >> 4; $output .= $itoa64[$c1]; $c1 = ($c2 & 0x0f) << 2; $c2 = ord($input[$i++]); $c1 |= $c2 >> 6; $output .= $itoa64[$c1]; $output .= $itoa64[$c2 & 0x3f]; } while (1); return $output; } function HashPassword($password) { $random = ''; if (CRYPT_BLOWFISH == 1 && !$this->portable_hashes) { $random = $this->get_random_bytes(16); $hash = crypt($password, $this->gensalt_blowfish($random)); if (strlen($hash) == 60) return $hash; } if (CRYPT_EXT_DES == 1 && !$this->portable_hashes) { if (strlen($random) < 3) $random = $this->get_random_bytes(3); $hash = crypt($password, $this->gensalt_extended($random)); if (strlen($hash) == 20) return $hash; } if (strlen($random) < 6) $random = $this->get_random_bytes(6); $hash = $this->crypt_private($password, $this->gensalt_private($random)); if (strlen($hash) == 34) return $hash; # Returning '*' on error is safe here, but would _not_ be safe # in a crypt(3)-like function used _both_ for generating new # hashes and for validating passwords against existing hashes. return '*'; } function CheckPassword($password, $stored_hash) { $hash = $this->crypt_private($password, $stored_hash); if ($hash[0] == '*') $hash = crypt($password, $stored_hash); return $hash == $stored_hash; } }

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  • Unable to verify body hash for DKIM

    - by Joshua
    I'm writing a C# DKIM validator and have come across a problem that I cannot solve. Right now I am working on calculating the body hash, as described in Section 3.7 Computing the Message Hashes. I am working with emails that I have dumped using a modified version of EdgeTransportAsyncLogging sample in the Exchange 2010 Transport Agent SDK. Instead of converting the emails when saving, it just opens a file based on the MessageID and dumps the raw data to disk. I am able to successfully compute the body hash of the sample email provided in Section A.2 using the following code: SHA256Managed hasher = new SHA256Managed(); ASCIIEncoding asciiEncoding = new ASCIIEncoding(); string rawFullMessage = File.ReadAllText(@"C:\Repositories\Sample-A.2.txt"); string headerDelimiter = "\r\n\r\n"; int headerEnd = rawFullMessage.IndexOf(headerDelimiter); string header = rawFullMessage.Substring(0, headerEnd); string body = rawFullMessage.Substring(headerEnd + headerDelimiter.Length); byte[] bodyBytes = asciiEncoding.GetBytes(body); byte[] bodyHash = hasher.ComputeHash(bodyBytes); string bodyBase64 = Convert.ToBase64String(bodyHash); string expectedBase64 = "2jUSOH9NhtVGCQWNr9BrIAPreKQjO6Sn7XIkfJVOzv8="; Console.WriteLine("Expected hash: {1}{0}Computed hash: {2}{0}Are equal: {3}", Environment.NewLine, expectedBase64, bodyBase64, expectedBase64 == bodyBase64); The output from the above code is: Expected hash: 2jUSOH9NhtVGCQWNr9BrIAPreKQjO6Sn7XIkfJVOzv8= Computed hash: 2jUSOH9NhtVGCQWNr9BrIAPreKQjO6Sn7XIkfJVOzv8= Are equal: True Now, most emails come across with the c=relaxed/relaxed setting, which requires you to do some work on the body and header before hashing and verifying. And while I was working on it (failing to get it to work) I finally came across a message with c=simple/simple which means that you process the whole body as is minus any empty CRLF at the end of the body. (Really, the rules for Body Canonicalization are quite ... simple.) Here is the real DKIM email with a signature using the simple algorithm (with only unneeded headers cleaned up). Now, using the above code and updating the expectedBase64 hash I get the following results: Expected hash: VnGg12/s7xH3BraeN5LiiN+I2Ul/db5/jZYYgt4wEIw= Computed hash: ISNNtgnFZxmW6iuey/3Qql5u6nflKPTke4sMXWMxNUw= Are equal: False The expected hash is the value from the bh= field of the DKIM-Signature header. Now, the file used in the second test is a direct raw output from the Exchange 2010 Transport Agent. If so inclined, you can view the modified EdgeTransportLogging.txt. At this point, no matter how I modify the second email, changing the start position or number of CRLF at the end of the file I cannot get the files to match. What worries me is that I have been unable to validate any body hash so far (simple or relaxed) and that it may not be feasible to process DKIM through Exchange 2010.

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  • How to "reduce" a hash?

    - by Julien Lebosquain
    Suppose I have any "long" hash, like a 16 bytes MD5 or a 20 bytes SHA1. I want to reduce this hash to fit on 4 bytes, for GetHashCode() purposes. First, I'm perfectly aware that I'll get more collisions. That's totally fine in my case, but I'd still prefer to get the less possible collisions. There are several solutions to my problem: I could take the 4 first bytes of the hash. I could take the 4 last bytes of the hash. I could take 4 random bytes of the hash. I could generate a hash of the hash, involving classic prime numbers multiplications. Are there other solutons I didn't think about? And more importantly, what method will give me the most unique hash code? I'm currently supposing they're almost equivalent. Microsoft choose that the public key token of an assembly is the last 8 bytes of the SHA1 hash of its public key, so I'll probably go for this solution but I'd like to know why.

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  • How do I interact with a Perl object that has a hash attribute?

    - by brydgesk
    I have a class with several variables, one of which is a hash (_runs): sub new { my ($class, $name) = @_; my $self = { _name => $name, ... _runs => (), _times => [], ... }; bless ($self, $class); return $self; } Now, all I'm trying to do is create an accessor/mutator, as well as another subroutine that pushes new data into the hash. But I'm having a hell of a time getting all the referencing/dereferencing/$self calls working together. I've about burned my eyes out with "Can't use string ("blah") as a HASH ref etc etc" errors. For the accessor, what is 'best practice' for returning hashes? Which one of these options should I be using (if any)?: return $self->{_runs}; return %{ $self->{_runs} }; return \$self->{_runs}; Further, when I'm using the hash within other subroutines in the class, what syntax do I use to copy it? my @runs = $self->{_runs}; my @runs = %{ $self->{_runs} }; my @runs = $%{ $self->{_runs} }; my @runs = $$self->{_runs}; Same goes for iterating over the keys: foreach my $dt (keys $self->{_runs}) foreach my $dt (keys %{ $self->{_runs} }) And how about actually adding the data? $self->{_runs}{$dt} = $duration; %{ $self->{_runs} }{$dt} = $duration; $$self->{_runs}{$dt} = $duration; You get the point. I've been reading articles about using classes, and articles about referencing and dereferencing, but I can't seem to get my brain to combine the knowledge and use both at the same time. I got my _times array working finally, but mimicking my array syntax over to hashes didn't work.

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  • NSClient++: external script with optional arguments

    - by syneticon-dj
    I am trying to define an external script which would take optional arguments in NSClient++ 0.4.1 on Windows. Following the nsclient-full.ini example code I have defined mycheck=cmd /C echo C:\mydir\myscript.ps1 %ARGS% | powershell.exe -command - which simply yields the string %ARGS% passed as the only argument to myscript.ps1, no matter what I specify in my call through NRPE (using Nagios' check_nrpe if that matters). I then tried to rewrite the definition to mycheck=cmd /C echo C:\mydir\myscript.ps1 $ARG1$ $ARG2$ | powershell.exe -command - (myscript.ps1 would take up to two arguments), which does help a bit. At least, if two arguments are provided, I can fetch them via the args[] array. The trouble starts when the call has less than two arguments - in this case the literal strings $ARG2 and $ARG1$ are passed through as arguments. Handling this case in the code of myscript.ps1 makes the whole argument processing routine ugly at best. Is there a sane way of defining optional parameters to an external script which would not pass NSClient's variable names if no parameter has been specified?

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