Egypt's police force is seeking to build a surveillance system to monitor social media for expressions of dissent – including profanity, immorality, insults and calls for strikes and protests.

According to a leaked document in which technology companies are invited to offer their services, Egypt's interior ministry says it wants the ability to scan Facebook, Twitter, WhatsApp and Viber in real-time for usage that might "harm public security or incite terrorism".

The ministry asks the unnamed companies for a system that could dredge up "vocabulary which is contrary to law and public morality". According to the document, this would include "degrading and acerbic ridicule; slander; insult; the use of profanity", incitement of "extremism, violence and rebellion … demonstrations, sit-ins and illegal strikes"; and "pornography and decadence; immorality and debauchery, and the publication of ways to manufacture explosives".

The leak drew immediate criticism from Egyptian rights activists and digital experts.

"They are using very vague and broad terms," said Ramy Raoof, a digital rights researcher who documents infringements of online freedoms in Egypt. "They think they are the only people who can judge people's opinions."

Files recovered from the offices of Egypt's looted intelligence services during the 2011 revolution revealed that the police already had technology that enabled them to hack and monitor computers belonging to individual dissidents and journalists.

In the first days of the uprising, the government also brought down all mobile networks in an attempt to stop the spread of messages on phones and social media.

But this leaked document, published in the normally pro-regime newspaper al-Watan, is the first hard proof that the Egyptian police seek to mass-monitor the content of those messages.

Among many other specifications, the police's preferred surveillance system would harbour the capacity to view allegedly problematic messages within 30 seconds of their publication; to recognise influential opinion-shapers within a certain geographic area; and to track how an individual's opinions changed over time.

Many of the specifications could be achieved with existing software, digital analysts said. "It's certainly feasible. It bears a lot of similarities to techniques used in existing data leakage technology," said Rik Ferguson, the security research director at Trend Micro, a digital security firm.

Ferguson named one firm that already provided similar services, and said it was comparable to the abilities of the NSA's tracking software, Prism. "The intent is the same, though smaller in scope," Ferguson said.

Since the leak, Egypt's interior minister, Mohammed Ibrahim, has confirmed that his staff are seeking to mass-monitor social media, but denied this would infringe civil liberties.

"The new system will not affect by any measure the freedom of opinion and expression," said Ibrahim, according to MENA, Egypt's state-run news agency.

Egypt's police have long been criticised for their heavy-handed tactics, which were a major cause of the 2011 revolution.

Since the overthrow of Mohamed Morsi as president in July 2013, they have achieved a partial rehabilitation in the eyes of Morsi's opponents. But many still condemn them for a crackdown on dissent in the months since, in which at least a thousand dissidents have been killed and more than 16,000 jailed.