Android Question Calculate the java.security.Key

KMatle said:

Take a look at the pem file:

View attachment 50552

1. It looks like a Base64-String
2. There's a header and a footer (which is not Base64)
3. There are LF's at the end of each line (which is not Base64, too)

What we need is a clean Base64 string:

B4X:

    Dim Pem As String
    Dim PemBytes() As Byte

    Pem=File.ReadString(File.DirApp,"pem.pem") 'read the pem file into a string
    Pem=Pem.Replace("-----BEGIN PRIVATE KEY-----","")
    Pem=Pem.Replace("-----END PRIVATE KEY-----","")
    Pem=Pem.Replace(CRLF,"")

After this it is:

B4X:

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...

This is a clean Base64-string

1. Convert it into Bytes
2. Load it

Full code:

B4X:

    Dim Pem As String
    Dim PemBytes() As Byte

    Pem=File.ReadString(File.DirApp,"pem.pem") 'load from file into string
    Pem=Pem.Replace("-----BEGIN PRIVATE KEY-----","")
    Pem=Pem.Replace("-----END PRIVATE KEY-----","")
    Pem=Pem.Replace(CRLF,"")
    Log(Pem)
    
    Dim su As StringUtils
    PemBytes=su.DecodeBase64(Pem) 'Base64 -> Bytes

    Dim TestC As Cipher
    Dim TestKPG As KeyPairGenerator
    TestC.Initialize("RSA/ECB/PKCS1Padding")
       TestKPG.Initialize("RSA", 2048)
    TestKPG.PrivateKeyFromBytes(PemBytes) 'Works!

Note: Usually you get the PUBLIC key, not the private one (you encrypt with it and it is DEcrypted with the private key). So if two programs use it, there will be 2 Public- and 2 Private Keys!

Click to expand...

Francesco Maresca said:

3 - Convert the key read from RSA PRIVATE KEY in PRIVATE KEY

Click to expand...

openssl genrsa  -out PrivateKey.pem 2048 'or higher
openssl pkcs8 -topk8 -inform pem -in PrivateKey.pem -outform pem -nocrypt -out C:/xampp/htdocs/rsa/PrivateKey.pem
openssl rsa -pubout -in PrivateKey.pem -out C:/xampp/htdocs/rsa/PublicKey.pem