Of revealing or publicizing either substantially true

Australia Victoria
The offence of blackmail is created by section 87^[13] of the Crimes Act 1958.
Sections 87(1) and (2) are derived from and identical to sections 21(1) and (2) of the Theft Act 1968 printed above.
Section 87(3) provides that a person guilty of blackmail is guilty of an indictable offence and liable to level 4 imprisonment (15 years maximum).
South Australia
The offence of blackmail is created by Part 6B Section 172^[14] of the Criminal Law Consolidation Act 1935.
Section 172 provides that a person who menaces another intending to get the other to submit to a demand is guilty of blackmail, and may be subject to imprisonment (a maximum of 15 years for a basic offence or a maximum of 20 years for an aggravated offence).
Republic of Ireland
The offence created by section 17(1)^[15] of the Criminal Justice (Public Order) Act, 1994 is described by the marginal note to that section as "blackmail, extortion and demanding money with menaces". The offence is derived from the offence under section 21 of the Theft Act 1968.
United Kingdom England and Wales
In England and Wales this offence is created by section 21(1) of the Theft Act 1968. Sections 21(1) and (2) of that Act provide:
(1) A person is guilty of blackmail if, with a view to gain for himself or another or with intent to cause loss to another, he makes any unwarranted demand with menaces; and for this purpose, a demand with menaces is unwarranted unless the person making it does so in the belief:
(a) that he has reasonable grounds for making the demand; and
(b) that the use of the menaces is a proper means of reinforcing the demand.
(2) The nature of the act or omission demanded is immaterial, and it is also immaterial whether the menaces relate to action to be taken by the person making the demand.
Construction
The Theft Act 1968 section 21 contains the present-day definition of blackmail in English law. It requires four elements:

1. 
   There must be a "demand".
   
2. 
   The demand must also have been accompanied or reinforced (at the time or later) by a "menace". Broadly, a menace is any threat, or implied consequence or action, which would coerce or pressure an unwilling person to accede (give in) to the demand.
   
3. 
   The making of a "demand with menace(s)" must have been "unwarranted". Broadly, a demand with menace is always unwarranted unless both the making of the demand was reasonably justified, and its reinforcement with the "menace" was proper, in the belief of the perpetrator.
   
4. 
   There must have been an intention by the perpetrator to make a gain for himself/herself or someone else, or to cause a loss to someone.
   

Therefore, the requirement for this offence may be paraphrased as:

1. 
   A person makes a demand of someone else, which is accompanied or reinforced in some way by some consequence if they don't comply, which would coerce an unwilling victim to do what is demanded,