C RSA encryption decryption with transmission

Question

I ve seen plenty of encryption decryption tutorials and examples on the net in C  that use the System Security Cryptography RSACryptoServiceProvider  but what I m hoping to be able to do is    Create an RSA public private keypair Transmit the public key  or for proof of concept  just move it in a string variable  Create a new RSA crypto provider and encrypt a string with the public key Transmit the encrypted string  or data  back to the original crypto provider and decrypt the string   Could anyone point me to a useful resource for this

User · Answer

public static string Encryption string strText                        var publicKey     lt RSAKeyValue gt  lt Modulus gt 21wEnTU mcD2w0Lfo1Gv4rtcSWsQJQTNa6gio05AOkV Er9w3Y13Ddo5wGtjJ19402S71HUeN0vbKILLJdRSES5MHSdJPSVrOqdrll vLXxDxWs U0UT1c8u6k Ogx9hTtZxYwoeYqdhDblof3E75d9n2F0Zvf6iTb4cI7j6fMs  lt  Modulus gt  lt Exponent gt AQAB lt  Exponent gt  lt  RSAKeyValue gt                 var testData   Encoding UTF8 GetBytes strText                using  var rsa   new RSACryptoServiceProvider 1024                                 try                                          client encrypting data with public key issued by server                                         rsa FromXmlString publicKey ToString                          var encryptedData   rsa Encrypt testData  true                        var base64Encrypted   Convert ToBase64String encryptedData                        return base64Encrypted                                    finally                                       rsa PersistKeyInCsp   false                                                     public static string Decryption string strText                        var privateKey     lt RSAKeyValue gt  lt Modulus gt 21wEnTU mcD2w0Lfo1Gv4rtcSWsQJQTNa6gio05AOkV Er9w3Y13Ddo5wGtjJ19402S71HUeN0vbKILLJdRSES5MHSdJPSVrOqdrll vLXxDxWs U0UT1c8u6k Ogx9hTtZxYwoeYqdhDblof3E75d9n2F0Zvf6iTb4cI7j6fMs  lt  Modulus gt  lt Exponent gt AQAB lt  Exponent gt  lt P gt  aULPE6jd5IkwtWXmReyMUhmI nfwfkQSyl7tsg2PKdpcxk4mpPZUdEQhHQLvE84w2DhTyYkPHCtq mMKE3MHw   lt  P gt  lt Q gt 3WV46X9Arg2l9cxb67KVlNVXyCqc w LWt tbhLJvV2xCF 0rWKPsBJ9MC6cquaqNPxWWEav8RAVbmmGrJt51Q   lt  Q gt  lt DP gt 8TuZFgBMpBoQcGUoS2goB4st6aVq1FcG0hVgHhUI0GMAfYFNPmbDV3cY2IBt8Oj uYJYhyhlaj5YTqmGTYbATQ   lt  DP gt  lt DQ gt FIoVbZQgrAUYIHWVEYi 187zFd7eMct Yi7kGBImJStMATrluDAspGkStCWe4zwDDmdam1XzfKnBUzz3AYxrAQ   lt  DQ gt  lt InverseQ gt QPU3Tmt8nznSgYZ 5jUo9E0SfjiTu435ihANiHqqjasaUNvOHKumqzuBZ8NRtkUhS6dsOEb8A2ODvy7KswUxyA   lt  InverseQ gt  lt D gt cgoRoAUpSVfHMdYXW9nA3dfX75dIamZnwPtFHq80ttagbIe4ToYYCcyUz5NElhiNQSESgS5uCgNWqWXt5PnPu4XmCXx6utco1UVH8HGLahzbAnSy6Cj3iUIQ7Gj 9gQ7PkC434HTtHazmxVgIR5l56ZjoQ8yGNCPZnsdYEmhJWk  lt  D gt  lt  RSAKeyValue gt                 var testData   Encoding UTF8 GetBytes strText                using  var rsa   new RSACryptoServiceProvider 1024                                 try                                                           var base64Encrypted   strText                          server decrypting data with private key                                         rsa FromXmlString privateKey                        var resultBytes   Convert FromBase64String base64Encrypted                       var decryptedBytes   rsa Decrypt resultBytes  true                       var decryptedData   Encoding UTF8 GetString decryptedBytes                       return decryptedData ToString                                      finally                                       rsa PersistKeyInCsp   false

User · Answer

well there are really enough examples for this  but anyway   here you go  using System  using System Security Cryptography   namespace RsaCryptoExample     static class Program         static void Main                 lets take a new CSP with a new 2048 bit rsa key pair       var csp   new RSACryptoServiceProvider 2048            how to get the private key       var privKey   csp ExportParameters true            and the public key           var pubKey   csp ExportParameters false            converting the public key into a string representation       string pubKeyString                    we need some buffer         var sw   new System IO StringWriter              we need a serializer         var xs   new System Xml Serialization XmlSerializer typeof RSAParameters              serialize the key into the stream         xs Serialize sw  pubKey             get the string from the stream         pubKeyString   sw ToString                     converting it back                   get a stream from the string         var sr   new System IO StringReader pubKeyString             we need a deserializer         var xs   new System Xml Serialization XmlSerializer typeof RSAParameters              get the object back from the stream         pubKey    RSAParameters xs Deserialize sr                    conversion for the private key is no black magic either     omitted          we have a public key     let s get a new csp and load that key       csp   new RSACryptoServiceProvider          csp ImportParameters pubKey            we need some data to encrypt       var plainTextData    foobar            for encryption  always handle bytes          var bytesPlainTextData   System Text Encoding Unicode GetBytes plainTextData            apply pkcs 1 5 padding and encrypt our data        var bytesCypherText   csp Encrypt bytesPlainTextData  false            we might want a string representation of our cypher text    base64 will do       var cypherText   Convert ToBase64String bytesCypherText                       some transmission   storage   retrieval                    and we want to decrypt our cypherText                    first  get our bytes back from the base64 string           bytesCypherText   Convert FromBase64String cypherText            we want to decrypt  therefore we need a csp and load our private key       csp   new RSACryptoServiceProvider          csp ImportParameters privKey            decrypt and strip pkcs 1 5 padding       bytesPlainTextData   csp Decrypt bytesCypherText  false            get our original plainText back          plainTextData   System Text Encoding Unicode GetString bytesPlainTextData                 as a side note  the calls to Encrypt   and Decrypt   have a bool parameter that switches between OAEP and PKCS 1 5 padding     you might want to choose OAEP if it s available in your situation

User · Answer

I ll share my very simple code for sample purpose  Hope it will help someone like me searching for quick code reference  My goal was to receive rsa signature from backend  then validate against input string using public key and store locally for future periodic verifications   Here is main part used for signature verification                       var signature   Get url      base64 encoded signature received from server         var inputtext   inputtext      this is main text signature was created for         bool result   VerifySignature inputtext  signature                    private bool VerifySignature string input  string signature                var result   false          using  var cps new RSACryptoServiceProvider                             converting input and signature to Bytes Arrays to pass to VerifyData rsa method to verify inputtext was signed using privatekey corresponding to public key we have below             byte   inputtextBytes   Encoding UTF8 GetBytes input               byte   signatureBytes    Convert FromBase64String signature                cps FromXmlString   lt RSAKeyValue gt  lt Modulus gt      lt  Modulus gt  lt Exponent gt      lt  Exponent gt  lt  RSAKeyValue gt        xml formatted publickey             result   cps VerifyData inputtextBytes   new SHA1CryptoServiceProvider    signatureBytes                        return result

User · Answer

Honestly  I have difficulty implementing it because there s barely any tutorials I ve searched that displays writing the keys into the files  The accepted answer was  fine   But for me I had to improve it so that both keys gets saved into two separate files  I ve written a helper class so y all just gotta copy and paste it  Hope this helps lol   using Microsoft Win32  using System  using System IO  using System Security Cryptography   namespace RsaCryptoExample       class RSAFileHelper               readonly string pubKeyPath    public key    change as needed         readonly string priKeyPath    private key    change as needed         public void MakeKey                           lets take a new CSP with a new 2048 bit rsa key pair             RSACryptoServiceProvider csp   new RSACryptoServiceProvider 2048                  how to get the private key             RSAParameters privKey   csp ExportParameters true                  and the public key                 RSAParameters pubKey   csp ExportParameters false                 converting the public key into a string representation             string pubKeyString                                  we need some buffer                 var sw   new StringWriter                      we need a serializer                 var xs   new System Xml Serialization XmlSerializer typeof RSAParameters                      serialize the key into the stream                 xs Serialize sw  pubKey                     get the string from the stream                 pubKeyString   sw ToString                    File WriteAllText pubKeyPath  pubKeyString                             string privKeyString                                  we need some buffer                 var sw   new StringWriter                      we need a serializer                 var xs   new System Xml Serialization XmlSerializer typeof RSAParameters                      serialize the key into the stream                 xs Serialize sw  privKey                     get the string from the stream                 privKeyString   sw ToString                    File WriteAllText priKeyPath  privKeyString                                   public void EncryptFile string filePath                          converting the public key into a string representation             string pubKeyString                                using  StreamReader reader   new StreamReader pubKeyPath   pubKeyString   reader ReadToEnd                                 get a stream from the string             var sr   new StringReader pubKeyString                  we need a deserializer             var xs   new System Xml Serialization XmlSerializer typeof RSAParameters                   get the object back from the stream             RSACryptoServiceProvider csp   new RSACryptoServiceProvider                csp ImportParameters  RSAParameters xs Deserialize sr                byte   bytesPlainTextData   File ReadAllBytes filePath                  apply pkcs 1 5 padding and encrypt our data              var bytesCipherText   csp Encrypt bytesPlainTextData  false                 we might want a string representation of our cypher text    base64 will do             string encryptedText   Convert ToBase64String bytesCipherText               File WriteAllText filePath encryptedText                     public void DecryptFile string filePath                          we want to decrypt  therefore we need a csp and load our private key             RSACryptoServiceProvider csp   new RSACryptoServiceProvider                 string privKeyString                                privKeyString   File ReadAllText priKeyPath                     get a stream from the string                 var sr   new StringReader privKeyString                     we need a deserializer                 var xs   new System Xml Serialization XmlSerializer typeof RSAParameters                      get the object back from the stream                 RSAParameters privKey    RSAParameters xs Deserialize sr                   csp ImportParameters privKey                             string encryptedText              using  StreamReader reader   new StreamReader filePath     encryptedText   reader ReadToEnd                  byte   bytesCipherText   Convert FromBase64String encryptedText                  decrypt and strip pkcs 1 5 padding             byte   bytesPlainTextData   csp Decrypt bytesCipherText  false                  get our original plainText back                File WriteAllBytes filePath  bytesPlainTextData

[c#] C# RSA encryption/decryption with transmission

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