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62 lines
1.6 KiB
62 lines
1.6 KiB
package crypto |
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import ( |
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"bytes" |
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"crypto/rsa" |
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"crypto/sha1" // #nosec G505 |
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"io" |
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"github.com/go-faster/errors" |
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) |
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// RSAEncryptHashed encrypts given data with RSA, prefixing with a hash. |
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func RSAEncryptHashed(data []byte, key *rsa.PublicKey, randomSource io.Reader) ([]byte, error) { |
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// Preparing `data_with_hash`. |
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// data_with_hash := SHA1(data) + data + (any random bytes); |
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// such that the length equals 255 bytes; |
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var dataWithHash [rsaWithHashLen]byte |
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if len(data) > rsaDataLen { |
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return nil, errors.Errorf("data length %d is too big", len(data)) |
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} |
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// Filling data_with_hash with random bytes. |
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if _, err := io.ReadFull(randomSource, dataWithHash[:]); err != nil { |
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return nil, err |
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} |
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h := sha1.Sum(data) // #nosec |
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// Replacing first 20 bytes with sha1(data). |
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copy(dataWithHash[:sha1.Size], h[:]) |
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// Replacing other bytes with data itself. |
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copy(dataWithHash[sha1.Size:], data) |
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// Encrypting "dataWithHash" with RSA. |
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res := rsaEncrypt(dataWithHash[:], key) |
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return res, nil |
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} |
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// RSADecryptHashed decrypts given data with RSA. |
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func RSADecryptHashed(data []byte, key *rsa.PrivateKey) ([]byte, error) { |
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var dataWithHash [rsaWithHashLen]byte |
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if !rsaDecrypt(data, key, dataWithHash[:]) { |
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return nil, errors.New("invalid data_with_hash") |
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} |
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hash := dataWithHash[:sha1.Size] |
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paddedData := dataWithHash[sha1.Size:] |
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// Guessing such data that sha1(data) == hash. |
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for i := 0; i <= len(paddedData); i++ { |
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data := paddedData[:len(paddedData)-i] |
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h := sha1.Sum(data) // #nosec |
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if bytes.Equal(h[:], hash) { |
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// Found. |
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return data, nil |
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} |
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} |
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// This can be caused by invalid keys or implementation bug. |
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return nil, errors.New("hash mismatch") |
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}
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