By Tim Franks
BBC News, Jerusalem
Shoes and clothes have recently been allowed into Gaza
BBC News has seen documents, submitted to an Israeli Court, which give more detail than ever before about how and why Israel maintains its Gaza blockade.
In one document, Israel describes the import curbs as "a central pillar in the armed conflict with Hamas".
It also confirms estimates were made of how many calories Gazans need, but says these were not used for policy-making.
Israel says the blockade is to pressure Hamas, which does not recognise Israel and backs attacks on its citizens.
Three years ago, after the Islamist Hamas movement seized power, Israel and Egypt tightened their closure of Gaza's borders, leaving the territory's 1.5 million inhabitants facing acute shortages.
But Israel has never published a list of banned items, saying it approves requests on a case-by-case basis.
Items allowed have changed over time, which has left humanitarian organisations and commercial importers constantly attempting to guess what will be approved.
The court case has been brought by the Israeli human rights group, Gisha.
The group has been trying, for more than a year, using freedom of information legislation, to squeeze information from the state about what exactly is allowed for import to Gaza, and why.
In January, Gisha, took the Israeli authorities to court, to try to force them to provide the information.
Gisha's director, Sari Bashi, says she is no security expert, "but preventing children from receiving toys, preventing manufacturers from getting raw materials - I don't see how that's responsive to Israeli security needs."
And she says that some of the prohibitions appear to be absurdly arbitrary: "I certainly don't understand why cinnamon is permitted, but coriander is forbidden. Is there something more dangerous about coriander? Is coriander more critical to Gaza's economy than cinnamon? This is a policy that appears to make no sense."
She argues that if there is a logic behind such decisions, the military should reveal what it is.
'Conflict against Hamas'
Now, after several months' waiting, the state has given its response to the court, in a written submission, seen by the BBC.
It throws a small pool of light on the process behind the blockade.
The overall rationale is set out, in bold type: "The limitation on the transfer of goods is a central pillar in the means at the disposal of the State of Israel in the armed conflict between it and Hamas."
The Israeli authorities also confirm the existence of four documents related to how the blockade works: how they process requests for imports into Gaza, how they monitor the shortages within Gaza, their approved list of what is allowed in, and a document entitled "Food Consumption in the Gaza Strip - Red Lines" which sets out the minimum calorie intake needed by Gaza's million and a half inhabitants, according to their age and sex.
This paper was however, the state insists, just a draft power-point presentation, used for "internal planning work", which "never served as a basis for the policy of the authority".
But while the first three documents promise a great deal of detail, that detail is not delivered.
In each case, the state argues that disclosure of what is allowed in and why would, in their words, "damage national security and harm foreign relations".
It offers, instead, to reveal the contents of the documents to the court in a private session with the judge.
The lack of clarity causes immense frustration not just among Gazans, but among aid groups, diplomats, and the United Nations - which has described Israel's blockade as "collective punishment"
The problem, they say, is not just the shortages themselves, but the unpredictability and changing nature of what is permitted for import.
Israeli officials have said, in the past, that they are concerned that building materials in particular could be misappropriated by Hamas for military ends.
But some Israeli commentators - even those who advocate a tough stance against Hamas - say that the strategy behind the much wider blockade is ill-defined, and harmful to Israel's international standing.
The BBC has received information from reliable sources that there are currently 81 items that are approved for import - from kidney beans to tinned meat - and as of March, shoes.
Among the large range of goods currently forbidden are jam, chocolate, wood for furniture, fruit juice, textiles, and plastic toys.
The 13-page submission by the Israeli authorities to the Tel Aviv District Court raises more questions than it answers.
It does set the context for the blockade: in what Israel considers to be its existential conflict with Hamas.
But it will not satisfy those calling for Israel to be more open about one of its most contentious policies.