# Difference between revisions of "SHA-1"

## 1 General Description

SHA-1 is an iterated hash function. It can be used to compute a 160-bit hash value for messages having a length of less than bits, cf. FIPS 180-2 Secure Hash Standard. As most iterated hash functions, SHA-1 applies MD strengthening.

### 1.1 Compression Function

The compression function processes input message blocks of 512 bits and produces a 160-bit chaining value. The compression function of SHA-1 basically consists of two parts: the message expansion and the state update transformation. The chaining variable (iv in the first iteration) is added to the output of the state update transformation (feed forward).

The SHA-1 compression function

#### 1.1.1 Message Expansion

In SHA-1, the message expansion is defined as follows. A single 512-bit input message block block is represented by 16 32-bit words, denoted by $M_i$, with $0 \leq i \leq 15$. The message input is linearly expanded into 80 32-bit words $W_i$ defined as follows:

## 3 Security Anaylsis

• Best know attack: by Wang et.al.
• Best known collision example: 64-step collision by De Canniere and Rechberger

something like: best know attack to date: kind of attack, which variant has been looked at (e.g. round-reduced), complexity, and reference to paper and abstract.

may be make here a new page with the other cryptanalysis results.