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Slow, stable, rectilinear crack propagation along the interface between a porous, elastic-plastic material and a rigid substrate is investigated. The Gurson model with constant porosity, and isotropic hardening is considered for the constitutive description of the ductile material. An asymptotic analysis of crack-tip fields is performed under steady-state, plane strain conditions. Two distinct solutions exist corresponding to predominantly tensile or shear mixed mode. Due to the higher hydrostatic stress state, the asymptotic solution reveals that the porosity influences only the stress fields of the tensile mode significantly. For high porosities the maximum of the hoop stress deviates from the interface line ahead of the crack-tip towards the porous ductile material, causing possible kinking of the fracture, so that the toughness of the interface crack may increase significantly.