The formula agreed between Indonesian and separatist rebel negotiators to end nearly 30 years of conflict in Aceh maintains the momentum for peace that has been building since December's tsunami devastated the province.

It is a fragile agreement that leaves challenges to be overcome on both sides.

Nonetheless, it is a triumph for common sense and good faith, in which the rebels dropped their demand for full independence in favour of achievable progress, and Jakarta has met them halfway – promising to withdraw its troops.

Under the pressure of the international focus on the ongoing disaster relief effort, the negotiators in Helsinki have drawn up a blueprint built on trust, until now missing between the two sides.

In the months ahead this will test the political skills of Indonesia's president and the authority of exiled rebel leaders over their forces on the ground in Aceh.

Full details of the memorandum of agreement to be signed on August 15 have still to emerge, but enough is known to show that although both sides have focused on areas on which they are able to agree, some delicate negotiations lie ahead.

President Susilo Bambang Yudhoyono has said that under the deal the rebels of the Free Aceh Movement (GAM) will hand in their weapons in return for an amnesty within three months of the signing, and that most of the 50,000 Indonesian troops in the region would then withdraw.

This is a significant concession from the GAM, unmatched by progressive equivalent withdrawals by a much larger opposing force. The credibility and powers of persuasion of the rebel leaders may be tested to the limit before it is fully honoured.

They will be relying on Dr Susilo to make progress with Jakarta's side of the bargain. The rebel delegation has revealed that the draft agreement allows them to form their own political party to contest local elections in Aceh.

This could be a key stumbling block because, as Dr Susilo's deputy Jusuf Kalla has pointed out, this will require a change in the law that provides only for national political parties represented in at least half the country's 33 provinces.

The change is likely to have the support of the largest bloc in parliament, Mr Kalla's Golkar, but Dr Susilo will have a harder time winning the support of nationalist and military factions.

Politically, Dr Susilo has a lot riding on the success of the accord. He is known for a mastery of consensus and he must call on every ounce of it to ensure that the peace deal is not derailed by military leaders more concerned with protecting corrupt vested interests in Aceh.

One positive that has emerged from the terrible tsunami is the triumph of the human spirit over unimaginable adversity. A truce and progress towards a lasting political settlement would be another. The people of Aceh deserve it.