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Validate KEY_DATA_BLOB_VERSION1 content in ExtractHKDF #71

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merged 1 commit into from
Oct 31, 2024
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Validate KEY_DATA_BLOB_VERSION1 content in ExtractHKDF #71

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13 changes: 9 additions & 4 deletions cng/hkdf.go
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Original file line number Diff line number Diff line change
Expand Up @@ -156,14 +156,19 @@ func ExtractHKDF(h func() hash.Hash, secret, salt []byte) ([]byte, error) {
return nil, errors.New("cng: unknown key data blob version")
}
// KEY_DATA_BLOB_VERSION1 format is:
// cbHash uint32 // Big-endian
// hashName [cbHash]byte
// cbHashName uint32 // Big-endian
// pHashName [cbHash]byte
// key []byte // Rest of the blob
Comment on lines 158 to 161
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Where does this format come from? I'm not able to find it anywhere.

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Hmm, I don't remember where the definition came from. Maybe I just inspected the content of the data and figured it out? I'll ask the CNG team to document this payload, just as other algorithm payloads are.

if len(blob) < 4 {
return nil, errors.New("cng: exported key is corrupted")
}
hashLength := binary.BigEndian.Uint32(blob[:])
return blob[4+hashLength:], nil
cbHashName := binary.BigEndian.Uint32(blob)
blob = blob[4:]
if len(blob) < int(cbHashName) {
return nil, errors.New("cng: exported key is corrupted")
}
// Skip pHashName.
return blob[cbHashName:], nil
}

func ExpandHKDF(h func() hash.Hash, pseudorandomKey, info []byte) (io.Reader, error) {
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