The usual answer goes thus: what is the probability that a rogue asteroid crashes on Earth within the next second, obliterating civilization-as-we-know-it, and killing off a few billion people? It can be argued that any unlucky event with a probability lower than that is not actually very important. If we have a “perfect” hash function … Read more
Yes, it is a hash mapping or hash table. You can read a description of python’s dict implementation, as written by Tim Peters, here. That’s why you can’t use something ‘not hashable’ as a dict key, like a list: >>> a = {} >>> b = [‘some’, ‘list’] >>> hash(b) Traceback (most recent call last): … Read more
You’re looking for Enumerable#select (also called find_all): @fathers.select {|father| father[“age”] > 35 } # => [ { “age” => 40, “father” => “Bob” }, # { “age” => 50, “father” => “Batman” } ] Per the documentation, it “returns an array containing all elements of [the enumerable, in this case @fathers] for which block is … Read more
No. MD5 is not encryption (though it may be used as part of some encryption algorithms), it is a one way hash function. Much of the original data is actually “lost” as part of the transformation. Think about this: An MD5 is always 128 bits long. That means that there are 2128 possible MD5 hashes. … Read more
“Hash and Range Primary Key” means that a single row in DynamoDB has a unique primary key made up of both the hash and the range key. For example with a hash key of X and range key of Y, your primary key is effectively XY. You can also have multiple range keys for the … Read more
The point of rainbow tables is that they’re created in advance and distributed en masse to save calculation time for others – it takes just as long to generate rainbow tables on the fly as it would to just crack the password+salt combination directly (since effectively what’s being done when generating rainbow tables is pre-running … Read more
The reason why Git and blockchains appear similar is because they are both using merkle trees as their underlying data structure. A merkle tree is a tree where each node is labeled with the cryptographic hash value of their contents, which includes the labels of its children. Git’s directed acyclic graph is exactly that, a … Read more
Update: Simply using a hash function is not strong enough for storing passwords. You should read the answer from Gilles on this thread for a more detailed explanation. For passwords, use a key-strengthening hash algorithm like Bcrypt or Argon2i. For example, in PHP, use the password_hash() function, which uses Bcrypt by default. $hash = password_hash(“rasmuslerdorf”, … Read more
The best implementation? That is a hard question because it depends on the usage pattern. A for nearly all cases reasonable good implementation was proposed in Josh Bloch‘s Effective Java in Item 8 (second edition). The best thing is to look it up there because the author explains there why the approach is good. A … Read more
Hashing a password once is insecure No, multiple hashes are not less secure; they are an essential part of secure password use. Iterating the hash increases the time it takes for an attacker to try each password in their list of candidates. You can easily increase the time it takes to attack a password from … Read more