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Derive KEY_SIZE from EC_CURVE when not explicitly provided #170

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Merged
JingMatrix merged 1 commit into from
Mar 21, 2026
Merged

Derive KEY_SIZE from EC_CURVE when not explicitly provided #170

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15 changes: 14 additions & 1 deletion app/src/main/java/org/matrix/TEESimulator/attestation/KeyMintAttestation.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -50,7 +50,8 @@ data class KeyMintAttestation(
algorithm = params.findAlgorithm(Tag.ALGORITHM) ?: 0,

// AOSP: [key_param(tag = KEY_SIZE, field = Integer)]
keySize = params.findInteger(Tag.KEY_SIZE) ?: 0,
// For EC keys, derive keySize from EC_CURVE when KEY_SIZE is absent.
keySize = params.findInteger(Tag.KEY_SIZE) ?: params.deriveKeySizeFromCurve(),

// AOSP: [key_param(tag = EC_CURVE, field = EcCurve)]
ecCurve = params.findEcCurve(Tag.EC_CURVE),
Expand Down Expand Up @@ -167,6 +168,18 @@ private fun Array<KeyParameter>.findAllKeyPurpose(tag: Int): List<Int> =
private fun Array<KeyParameter>.findAllDigests(tag: Int): List<Int> =
this.filter { it.tag == tag }.map { it.value.digest }

/** Derives keySize from EC_CURVE tag when KEY_SIZE is not explicitly provided. */
private fun Array<KeyParameter>.deriveKeySizeFromCurve(): Int {
val curveId = this.find { it.tag == Tag.EC_CURVE }?.value?.ecCurve ?: return 0
return when (curveId) {
EcCurve.P_224 -> 224
EcCurve.P_256, EcCurve.CURVE_25519 -> 256
EcCurve.P_384 -> 384
EcCurve.P_521 -> 521
else -> 0
}
}

/**
* Derives the EC Curve name. Logic: Checks specific EC_CURVE tag first (field=EcCurve), falls back
* to KEY_SIZE (field=Integer).
Expand Down
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