**Connected: An Internet Encyclopedia**

*3.1 Step 1. Append Padding Bits*

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RFC 1321

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3. MD5 Algorithm Description

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**Next:** 3.2 Step 2. Append Length

### 3.1 Step 1. Append Padding Bits

3.1 Step 1. Append Padding Bits
The message is "padded" (extended) so that its length (in bits) is
congruent to 448, modulo 512. That is, the message is extended so
that it is just 64 bits shy of being a multiple of 512 bits long.
Padding is always performed, even if the length of the message is
already congruent to 448, modulo 512.

Padding is performed as follows: a single "1" bit is appended to the
message, and then "0" bits are appended so that the length in bits of
the padded message becomes congruent to 448, modulo 512. In all, at
least one bit and at most 512 bits are appended.

**Next:** 3.2 Step 2. Append Length

**Connected: An Internet Encyclopedia**

*3.1 Step 1. Append Padding Bits*