hash | 易学教程

Best general-purpose digest function?

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问题 When writing an average new app in 2009, what's the most reasonable digest function to use, in terms of security and performance? (And how can I determine this in the future, as conditions change?) When similar questions were asked previously, answers have included SHA1, SHA2, SHA-256, SHA-512, MD5, bCrypt, and Blowfish. I realize that to a great extent, any one of these could work, if used intelligently, but I'd rather not roll a dice and pick one randomly. Thanks. 回答1: I'd follow NIST/FIPS

史上最详细的HashTable源码解析，最容易懂

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HashTable源码分析更多资源和教程请关注公众号：非科班的科班。如果觉得我写的还可以请给个赞，谢谢大家，你的鼓励是我创作的动力 ###1.前言 Hashtable 一个元老级的集合类，早在 JDK 1.0 就诞生了 ###1.1.摘要在集合系列的第一章，咱们了解到，Map 的实现类有 HashMap、LinkedHashMap、TreeMap、IdentityHashMap、WeakHashMap、HashTable、Properties 等等。 ###1.2.简介 Hashtable 一个元老级的集合类，早在 JDK 1.0 就诞生了，而 HashMap 诞生于 JDK 1.2，在实现上，HashMap 吸收了很多 Hashtable 的思想，虽然二者的底层数据结构都是数组 + 链表结构，具有查询、插入、删除快的特点，但是二者又有很多的不同。 打开 Hashtable 的源码可以看到，Hashtable 继承自 Dictionary，而 HashMap 继承自 AbstractMap。 public class Hashtable<K,V> extends Dictionary<K,V> implements Map<K,V>, Cloneable, java.io.Serializable { ..... } HashMap 继承自 AbstractMap

How can I implement a fixed size hashmap?

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问题 I want to implement a hashmap, but I am not allowed to let it expand. Since I do know that I need to store at most N elements, I could pre-allocate an array with N elements for each bucket of my hashtable, so that I can still store N elements in the worst case where all keys are hashed on the same bucket. But the elements that I need to store are rather big, so for large N this is very inefficient use of memory. Is it possible to implement a hashmap efficiently (in terms of memory) with a

Case Insensitive hash (SHA) of a string

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问题 I’m passing a name string and its SHA1 value into a database. The SHA value is used as an index for searches. After the implementation was done, we got the requirement to make searching the name case insensitive. We do need to take all languages into account (Chinese characters are a real use case). I know about the Turkey Test. How can I transform my input string before hashing to be case insensitive? Ideally I’d like it to be equivalent of InvariantCultureIgnoreCase. In other words, how do

shiro with jdbc and hashed passwords

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问题 Here is my shiro config [main] authc.loginUrl = /site/index.jsp authc.usernameParam = user authc.passwordParam = pass authc.rememberMeParam = remember authc.successUrl = /site/home.jsp jdbcRealm=org.apache.shiro.realm.jdbc.JdbcRealm jdbcRealm.permissionsLookupEnabled=true jdbcRealm.authenticationQuery = select password from users where username = ? jdbcRealm.userRolesQuery = select role from users where username = ? credentialsMatcher = org.apache.shiro.authc.credential

need help in getting nested ruby hash hierarchy

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问题 I have hash deep nested hash and i want the hierarchy(parent to child) for each key as an array. for example - hash = { "properties"=>{ "one"=>"extra", "headers"=>{ "type"=>"object", "type1"=>"object2" }, "entity"=>{ "type"=>"entype" }, }, "sec_prop"=>"hmmm" } for this hash I want output as given below, as a separate array for each key. [properties,one] [properties,headers,type] [properties,headers,type1] [properties,entity,type] [sec_prop] i have been trying and searching this for so long

Best suited data-structure for prefix based searches

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问题 I have to maintain a in-memory data-structure of Key-Value pair. I have following constraints: Both key and values are text strings of length 256 and 1024 respectively. Any key generally looks like k1k2k3k4k5, each k(i) being 4-8 byte string in itself. As far as possible, in-memory data-structure should have contiguous memory. I have 400 MB worth of Key-Value pair and am allowed 120% worth of allocation. (Additional 20% for metadata, only if needed.) DS will have following operations: Add

How do I convert a large string into hex and then into byte?

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问题 I work with cellphones and deal with MEID numbers on a daily basis. So instead of searching online for a MEID (a hex number of length 14) to pseudo ESN (a hex number of length 8) calculator, I figured I can make my own program. The way to obtain a pESN from MEID is fairly simple in theory. For example, given MEID 0xA0000000002329, to make a pESN, SHA-1 needs to be applied to the MEID. SHA-1 on A0000000002329 gives e3be267a2cd5c861f3c7ea4224df829a3551f1ab. Take the last 6 hex numbers of this

What kind of hash does mysql use?

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问题 I'm writing my own code similar to phpMyAdmin. But I'll need the user to be able to sign on using their username and password from the mysql database. I need to know what kind of hash the mysql database uses to store each users password. I checked dev.mysql.com for answers but couldnt find anything, other than its the newer 41 byte hash beginning with an *. 回答1: I don't think you will be able to decrypt password stoed in MySQL table and it's of no use using password which is stored in mysql .

What is the benefit of a “random” salt over a “unique” salt?

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问题 I am currently writing a program and part of it involves securely creating password hashes to store in a database and I came across the phpass framework, which seems to be highly recommended. In phpass, they seem to go through great lengths to produce a salt that is as truly random as possible to be used for the hashes (e.g. reading from /dev/urandom). My question is, what is the benefit of doing this as opposed to simply using uniqid() ? Isn't the point simply to make sure that the salts