Hashing

This work is licensed with a
Creative Commons Attribution 4.0 International License

This material was developed with funding
from the National Science Foundation

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Hashing

This work is licensed with a Creative Commons Attribution 4.0 International LicenseEndFragment

This material was developed with funding from the National Science Foundation

Input

Output

Hash Function

The hash value, or digest, is a one-way result. This means that you cannot figure out what the input was even if you are given the output and you know the mathematical algorithm used. Additonally, you cannot determine the input by analyzing the output or running it through another function.

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e75abac16d95c4a18c4d00004f360639

The hash function generates a fixed size output called the hash value or digest. A hash algorithm, such as MD5, produces the same sized output no matter what the size of the input. The MD5 algorithm produces a 128-bit hash value for each data source.

password hash value

5f4dcc3b5aa765d61d8327deb882cf99

string hash value

The quick brown fox jumped over the lazy dog.

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image hash value

MD5

b8781521d6281234ae6af85d2a75ded0

>>click on each input

documents hash value

bcca5a7c204655a389e3513767463843

application download hash value

5c6ffbdd40d9556b73a21e63c3e0e904

15e771d2caacdf2e70e5925361a1770508e2a66130f20e113df78f778685701b

A hash has several characteristics. The first is that given an input and a hash algorithm, the hash algorithm will always produce the same hash value as its output.

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The missing period generates a different hash value for the character string

The quick brown fox jumped over the lazy dog

08a008a01d498c404b0c30852b39d3b8

The hash process validates data integrity (meaning that the data has not changed). If the input data changes in any way, the output hash value will be different. Hashes can validate the data being transmitted or it can prove that the data was not tampered with.

click on the grinder to calculate the hash values

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Boolean Logic

All hashing functions inclue a predefined mathematical operation and/or logical computations such as Boolean logic to generate a hash digest of a fixed size.

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Complex

Click on each type of hash function

Mathematical

Transmission Integrity Check

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File Verification

Practical Applications

Password Verification

Password Storage

Evidence Tampering Prevention

Character String

ed4756cd

0e660de2dc10d8f31f78776f34ebc6fc

Image

Audio File

Hash Value

>>click on each component of the hashing process

Any type of data

Video

Password

The mathematical or logical operation

Hash Function

A fixed-size numeric representation of the input’s contents

1582054665

Documents

Downloaded File

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Hashing is the process of converting an input of any length using a mathematical or logical function into a fixed-sized output called a hash value or hash digest.

93a6bc0e0b9b7cecf30d0a1303a1da3621088f55dd3f9251b48e55b198a63902

A computer stores all data types as binary data. Hashes work on the binary data directly no matter what type of input is hashed.

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0000 1101

Adding: 0100 0001 = 65 0100 0010 = 66 0100 0011 = 67 0100 0100 = 68

The secret to how the hash function generates a fixed-size digest is in the extracting of the results. This checksum function adds the binary numbers together to calculate a sum, and uses only the first eight bits as the digest. The same message digest will result every time the process is repeated.

click on password to continue

Password is ABCD

no carry over--only uses eight least significant digits

A = 0100 0001 B = 0100 0010 C = 0100 0011 D = 0100 0100

click grinder to continue

1 0000 1101 = 266

0000 0100

Another way to generate f fixed-size digest is to use a Boolean opeation (AND, OR, XOR). The XOR operation is the most common. Again, the message digest will always be the same when given the same input.

XOR=030100 0011 = 67 XOR=64

XOR0100 0001 = 65 0100 0010 = 66 XOR=03

XOR=640100 0100 = 68

= 136

130 + 132 + 134 + 136 = 664

= 130

664 = 0010 1001 1000

1001 1000 = 98

Shift 65 1000001

Shift 67 1000011

Complex function: rotated then added 0100 0001 = 65 0100 0010 = 66 0100 0011 = 67 0100 0100 = 68

Shift 66 1000010

= 132

0010 1001 1000

Shift 68 1000100

A complex operation rotates the data before summing the results. Each input byte rotates by one bit. The most significant bit on the left takes the least significant position on the right. All other bits shift one position to the left. Then you sum all of the bytes. The first eight bits are used as the digest.

= 134

Hashing

Password Created:

Bob creates his password. The system hashes the password, and the message digest is what actually gets stored on the system. Bob’s actual password is NOT saved on the system.

G00dDog

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The system stores Bob’s password as a hash. The next time he enters his password, the password gets hashed and compared to the hash stored in the authentication table. If the hashes do not match, the user is denied access.

Password Entered:

Hash saved for G00dDog

GoodDog

Bernie

Bob is the payroll administrator for ACME, and he is currently updating the Payroll Report. Since this file is also used by several others in the organization, Bob performs a hash on the file and saves the results. Anyone else that performs a hash on the file will receive the same hash value and knows that the file has not been changed and its integrity has been maintained.

Click Bernie to continue

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Bernie sends data to Bob. Bernie’s system segments and organizes the data into data units called packets. After forming each packet, it calculates a hash based on the binary data in that packet. The hash gets appended to the packet, and the frame gets transmitted. When Bob receives the packet, his system verifies its content using the hash appended to the data unit. If the data was corrupted during transmission, the hash values will not match. Bob’s device will request that any corrupted packet be re-transmitted. This provides for trustworthy communication and save bandwidth by only retransmitting corrupted packets instead of the entire file.

Bob

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Resend packet 3/4

cd8ed4eebac3c7dc5c0644f5a3e27e8

<< click on locker to open

Bernie confiscated a hard drive as evidence from a crime scene. He will use a hash function to obtain a hash digest before storing the drive in the evidence locker. When Bob, the forensic analyst, goes to begin his investigation, he will use that hash digest to ensure that this evidence has not been tampered with.