No, a UN tribunal to investigate the flotilla massacre has ruled that it is legal, headed by failed politician Geoffrey Palmer and human rights abuser Uribe. The blockade is illegal due to it's violation of San Remo ie that humanitarian aid and necessities are not witheld from a civilian population. Israel can try to spin it as legal but international lawyers disagree.
U.S. defense contractor accused of copying secret military documents (Reuters)
from the article: Gaza-bound ship carrying pro-Palestinian activists sets sail from Greece