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Add functionality for DLOC/LOC decryption of assignment and entry data
Currently, we follow a naive approach. Both DecryptAssignmentData() and DecryptEntryData() take a list of matched (by pi) DLOC/LOC ciphertexts and encrypted assignment/entry data. We decrypt the DLOC/LOC ciphertexts to get the (U, S, c_x), where x = a|e, tuples and then attempt to interpolate all (U, S) pairs to find k. The problem is that if we are given one malformed pair, the entire process fails. This is a problem that can easily be fixed if we implement the smarter algorithm mentioned in the paper (see issue #5). If we assume no malicious (U, S) pairs, then the process finds k and correctly decrypts c_x to get the assignment/entry key that can be used to decrypt the data given. + Update main.go to show this decryption process
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,193 @@ | ||
| package callisto | ||
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| import ( | ||
| "crypto/rsa" | ||
| "fmt" | ||
|
|
||
| ss "github.com/superarius/shamir" | ||
| ff "github.com/superarius/shamir/modular" | ||
|
|
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| "github.com/vmihailenco/msgpack" | ||
|
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| "github.com/ymarcus93/gallisto/encoding" | ||
| "github.com/ymarcus93/gallisto/encryption" | ||
| "github.com/ymarcus93/gallisto/shamir" | ||
| "github.com/ymarcus93/gallisto/types" | ||
| ) | ||
|
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| // DecryptAssignmentData decrypts a list of encrypted assignment data. It does | ||
| // this by finding a common k value amongst matched dlocData and attempting to | ||
| // decrypt encrypted assignment keys with this k. It then uses the decrypted | ||
| // assignment keys to decrypt all assignment data. | ||
| func DecryptAssignmentData(dlocCiphertexts [][]byte, encryptedAssignmentData []types.GCMCiphertext, dlocPrivateKey *rsa.PrivateKey) ([]types.AssignmentData, error) { | ||
| if len(dlocCiphertexts) != len(encryptedAssignmentData) { | ||
| return nil, fmt.Errorf("mismatch length between dlocCiphertexts and encrypted assignment data") | ||
| } | ||
|
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| // Decrypt dloc ciphertexts | ||
| dlocData, err := decryptLOCCiphertexts(dlocCiphertexts, dlocPrivateKey) | ||
| if err != nil { | ||
| return nil, fmt.Errorf("failed to decrypt DLOC ciphertexts: %v", err) | ||
| } | ||
|
|
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| // Validate | ||
| if !validateLOCData(dlocData, types.Director) { | ||
| return nil, fmt.Errorf("decrypted DLOC ciphertexts but found non-Director data") | ||
| } | ||
|
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||
| // Find k | ||
| kAsBytes, err := findKValueFromLOCData(dlocData) | ||
| if err != nil { | ||
| return nil, fmt.Errorf("failed to find k value from DLOC ciphertexts: %v", err) | ||
| } | ||
|
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| // Decrypt assignment data | ||
| assignmentDatas := make([]types.AssignmentData, len(dlocData)) | ||
| for i, d := range dlocData { | ||
| k_a, err := encryption.DecryptAES(kAsBytes, d.EncryptedKey) | ||
| if err != nil { | ||
| return nil, fmt.Errorf("failed to decrypt EncryptedAssignmentDataKey at index %v: %v", i, err) | ||
| } | ||
| assignData, err := symDecryptAssignmentData(encryptedAssignmentData[i], k_a) | ||
| if err != nil { | ||
| return nil, fmt.Errorf("failed to decrypt assignment data at index %v: %v", i, err) | ||
| } | ||
| assignmentDatas[i] = assignData | ||
| } | ||
|
|
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| return assignmentDatas, nil | ||
| } | ||
|
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| // DecryptEntryData decrypts a list of encrypted entry data. It does this by | ||
| // finding a common k value amongst matched locData and attempting to decrypt | ||
| // encrypted entry keys with this k. It then uses the decrypted entry keys to | ||
| // decrypt all entry data. | ||
| func DecryptEntryData(locCiphertexts [][]byte, encryptedEntryData []types.GCMCiphertext, locPrivateKey *rsa.PrivateKey) ([]types.EntryData, error) { | ||
| if len(locCiphertexts) != len(encryptedEntryData) { | ||
| return nil, fmt.Errorf("mismatch length between locCiphertexts and encrypted entry data") | ||
| } | ||
|
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||
| // Decrypt loc ciphertexts | ||
| locData, err := decryptLOCCiphertexts(locCiphertexts, locPrivateKey) | ||
| if err != nil { | ||
| return nil, fmt.Errorf("failed to decrypt LOC ciphertexts: %v", err) | ||
| } | ||
|
|
||
| // Validate | ||
| if !validateLOCData(locData, types.Counselor) { | ||
| return nil, fmt.Errorf("decrypted LOC ciphertexts but found non-Counselor data") | ||
| } | ||
|
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||
| // Find k | ||
| kAsBytes, err := findKValueFromLOCData(locData) | ||
| if err != nil { | ||
| return nil, fmt.Errorf("failed to find k value from LOC ciphertexts: %v", err) | ||
| } | ||
|
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| // Decrypt entry data | ||
| entryDatas := make([]types.EntryData, len(locData)) | ||
| for i, d := range locData { | ||
| k_e, err := encryption.DecryptAES(kAsBytes, d.EncryptedKey) | ||
| if err != nil { | ||
| return nil, fmt.Errorf("failed to decrypt EncryptedEntryDataKey at index %v: %v", i, err) | ||
| } | ||
| entryData, err := symDecryptEntryData(encryptedEntryData[i], k_e) | ||
| if err != nil { | ||
| return nil, fmt.Errorf("failed to decrypt entry data at index %v: %v", i, err) | ||
| } | ||
| entryDatas[i] = entryData | ||
| } | ||
|
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| return entryDatas, nil | ||
| } | ||
|
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| func validateLOCData(data []types.LOCData, expectedLOCType types.LOCType) bool { | ||
| for _, d := range data { | ||
| if d.Type != expectedLOCType { | ||
| return false | ||
| } | ||
| } | ||
| return true | ||
| } | ||
|
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| func decryptLOCCiphertexts(locCiphertexts [][]byte, privateKey *rsa.PrivateKey) ([]types.LOCData, error) { | ||
| // Decrypt ciphertexts to get all loc data | ||
| locData := make([]types.LOCData, len(locCiphertexts)) | ||
| for i, c := range locCiphertexts { | ||
| decryptedCiphertext, err := decryptLOCCiphertext(c, privateKey) | ||
| if err != nil { | ||
| return nil, fmt.Errorf("failed to decrypt (D)LOC ciphertext at index %v: %v", i, err) | ||
| } | ||
| locData[i] = decryptedCiphertext | ||
| } | ||
|
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| return locData, nil | ||
| } | ||
|
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| func findKValueFromLOCData(locData []types.LOCData) ([]byte, error) { | ||
| // Form shamir (x,y) shares | ||
| shares := make([]*ss.Share, len(locData)) | ||
| for i, d := range locData { | ||
| shares[i] = &ss.Share{ | ||
| X: ff.IntFromBytes(d.U), | ||
| Y: ff.IntFromBytes(d.S), | ||
| } | ||
| } | ||
|
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| // Find K Value (the key) | ||
| kAsElement, err := shamir.FindShamirKValue(shares) | ||
| if err != nil { | ||
| return nil, fmt.Errorf("failed to find k value: %v", err) | ||
| } | ||
| return kAsElement.Bytes(), nil | ||
| } | ||
|
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| func decryptLOCCiphertext(locCiphertext []byte, privateKey *rsa.PrivateKey) (types.LOCData, error) { | ||
| // Decrypt ciphertext | ||
| dlocDataBytes, err := encryption.DecryptRSA(locCiphertext, privateKey) | ||
| if err != nil { | ||
| return types.LOCData{}, fmt.Errorf("failed to decrypt (D)LOC ciphertext: %v", err) | ||
| } | ||
|
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| // Decode msgpack encoding of LOC data | ||
| dlocData, err := encoding.DecodeLOCData(dlocDataBytes) | ||
| if err != nil { | ||
| return types.LOCData{}, err | ||
| } | ||
|
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| return dlocData, nil | ||
| } | ||
|
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| func symDecryptAssignmentData(encryptedAssignmentData types.GCMCiphertext, assignmentDataKey []byte) (types.AssignmentData, error) { | ||
| // Decrypt assignment data | ||
| assignmentDataEncodedBytes, err := encryption.DecryptAES(assignmentDataKey, encryptedAssignmentData) | ||
| if err != nil { | ||
| return types.AssignmentData{}, fmt.Errorf("failed to decrypt assignment data: %v", err) | ||
| } | ||
|
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| // Decode msgpack encoding | ||
| var decodedAssignmentData types.AssignmentData | ||
| err = msgpack.Unmarshal(assignmentDataEncodedBytes, &decodedAssignmentData) | ||
| if err != nil { | ||
| return types.AssignmentData{}, fmt.Errorf("failed to decode assignment data: %v", err) | ||
| } | ||
|
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| return decodedAssignmentData, nil | ||
| } | ||
|
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| func symDecryptEntryData(encryptedEntryData types.GCMCiphertext, entryDataKey []byte) (types.EntryData, error) { | ||
| // Decrypt entry data | ||
| assignmentDataEncodedBytes, err := encryption.DecryptAES(entryDataKey, encryptedEntryData) | ||
| if err != nil { | ||
| return types.EntryData{}, fmt.Errorf("failed to decrypt entry data: %v", err) | ||
| } | ||
|
|
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| // Decode msgpack encoding | ||
| var decodedEntryData types.EntryData | ||
| err = msgpack.Unmarshal(assignmentDataEncodedBytes, &decodedEntryData) | ||
| if err != nil { | ||
| return types.EntryData{}, fmt.Errorf("failed to decode entry data: %v", err) | ||
| } | ||
|
|
||
| return decodedEntryData, nil | ||
| } |
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