user10621: I am looking for a technical answer that explains how are validated the forged block.
I already looked in the NXT wiki and in their white paper and found no detailed explanation.

user18526: Below is an explanation how forging works at the current moment, in the future this will be slightly changed.
Every block has two fields - BlockSignature and GenerationSignature.
The former is filled by signing the block data with the private key of an account that generated a block and has almost nothing to do with forging process.
The latter is filled by computing SHA256(GenerationSignatureOfPreviousBlock+PublicKeyOfAccount).
The first 8 bytes of the hash give an unsigned 64-bit number in little-endian format, this number is called "hit".
Every account has a so-called EffectiveBalance which is usually (but not always) higher if the account holds more coins. EffectiveBalance is multiplied by some value that is the same for all the accounts - BaseTarget (it's adjusted every block trying to keep block generation rate at 1 minute) - and by number of seconds that have passed since the previous block. The resulting value is called "target".
If "hit" is less than "target" then peers accept a block and attach it to the blockchain.
This is the essential part of forging. I omitted such obvious things as validation of transaction signatures, checks for double-spending, etc.

10621: <p>I am looking for a technical answer that explains how are validated the forged block.</p>

<p>I already looked in the NXT wiki and in their white paper and found no detailed explanation.</p>
 18526: <p>Below is an explanation how forging works at the current moment, in the future this will be slightly changed.</p>

<p>Every block has two fields - BlockSignature and GenerationSignature.</p>

<p>The former is filled by signing the block data with the private key of an account that generated a block and has almost nothing to do with forging process.</p>

<p>The latter is filled by computing SHA256(GenerationSignatureOfPreviousBlock+PublicKeyOfAccount).</p>

<p>The first 8 bytes of the hash give an unsigned 64-bit number in little-endian format, this number is called "hit".</p>

<p>Every account has a so-called EffectiveBalance which is usually (but not always) higher if the account holds more coins. EffectiveBalance is multiplied by some value that is the same for all the accounts - BaseTarget (it's adjusted every block trying to keep block generation rate at 1 minute) - and by number of seconds that have passed since the previous block. The resulting value is called "target".</p>

<p>If "hit" is less than "target" then peers accept a block and attach it to the blockchain.</p>

<p>This is the essential part of forging. I omitted such obvious things as validation of transaction signatures, checks for double-spending, etc.</p>
