decrypt rsa string

[victor11109]

hi.
im trying few days to decrypt an rsa pkca1 encrypted string with privatekey . but no success 
i used openssl unit . and also lockbox library .

currently im using this code in python

Code: Python  [Select][+][-]

1. from Crypto.PublicKey import RSA
2. from Crypto.Cipher import PKCS1_v1_5
3. import base64
4.  
5. # Load private key
6. private_key = RSA.import_key(open('private_key.pem').read())
7.  
8. # Encrypted text (assuming it's base64-encoded)
9. encrypted_text_base64 = "some_encrypted_text"
10.  
11. # Decode base64
12. ciphertext = base64.b64decode(encrypted_text_base64)
13.  
14. # Create a PKCS1_v1_5 cipher object
15. cipher = PKCS1_v1_5.new(private_key)
16.  
17. # Decrypt the ciphertext
18. plaintext = cipher.decrypt(ciphertext, None)
19.  
20. print("Decrypted plaintext:", plaintext.decode('utf-8'))
21.  

its working fine . but wnat same functionaly in pascal .

the code that writed in lazarus is

Code: Pascal  [Select][+][-]

1. program project1;
2.  
3. uses
4.   Classes,
5.   SysUtils,
6.   openssl,
7.   base64;
8.  
9.   function DecryptRSA(const EncryptedData: ansistring; const PrivateKey: ansistring): ansistring;
10.   var
11.     RSAKey: pRSA;
12.     Bio: pBIO;
13.     DecryptedLen: integer;
14.     DecryptedData: array of byte;
15.   begin
16.     Bio := BIO_new_mem_buf(@PrivateKey[1], Length(PrivateKey));
17.     RSAKey := PEM_read_bio_PrivateKey(Bio, nil, nil, nil);
18.     SetLength(DecryptedData, RSA_size(RSAKey));
19.     DecryptedLen := RSA_private_decrypt(Length(EncryptedData), @EncryptedData[1], @DecryptedData[0], RSAKey, RSA_PKCS1_PADDING);
20.     Result := ansistring(Copy(ansistring(DecryptedData), 1, DecryptedLen));
21.   end;
22.  
23.  
24. var
25.   EncryptedString, PrivateKey: ansistring;
26.   DecryptedString: ansistring;
27. begin
28.   EncryptedString := DecodeStringBase64('...');
29.   PrivateKey := '...';
30.   DecryptedString := DecryptRSA(EncryptedString, PrivateKey);
31.   WriteLn('Decrypted Data: ', DecryptedString);
32. end.
33.  

but not working .

[victor11109]

UPDATE : after spend some time finally solved by my self 

Code: Pascal  [Select][+][-]

1. program Project1;
2.  
3. uses
4.   Classes,
5.   SysUtils,
6.   openssl,
7.   base64;
8.  
9. var
10.   rsa: PRSA;
11.   bio: PBIO;
12.   pkey: PEVP_PKEY;
13.   privateKeyFile, encryptedText: string;
14.   buf, decryptedBuf: TBytes;
15.   len: integer;
16. begin
17.   privateKeyFile := 'pvkey.pem';
18.   encryptedText := DecodeStringBase64('encrypted_text');
19.  
20.   bio := BIO_new_file(PChar(privateKeyFile), 'r');
21.   pkey := PEM_read_bio_PrivateKey(bio, nil, nil, nil);
22.   rsa := PRSA(pkey^.attributes);
23.  
24.   len := RSA_size(rsa);
25.   SetLength(decryptedBuf, len);
26.   len := RSA_private_decrypt(len, @encryptedText[1], @decryptedBuf[0], rsa, RSA_PKCS1_PADDING);
27.  
28.   WriteLn(StringOf(decryptedBuf));
29.   ReadLn;
30. end.
31.  

but i have question in  line that get rsa key from PEVP_PKEY  " rsa := PRSA(pkey^.attributes); " - is this actual way to do this ?

[TRon]

but i have question in  line that get rsa key from PEVP_PKEY  " rsa := PRSA(pkey^.attributes); " - is this actual way to do this ?

No it isn't (but to my knowledge, it isn't exactly wrong either).

There used to be a function named EVP_PKEY_get0_RSA (e.g. : "const RSA *EVP_PKEY_get0_RSA(const EVP_PKEY *pkey);"  ) but that seems to be deprecated.

My google-foo seems off today (seem to be getting normal for me these days  :'( ) because I failed to find an answer that is better suited... so in that regards your solution is as good as any ?

[victor11109]

but i have question in  line that get rsa key from PEVP_PKEY  " rsa := PRSA(pkey^.attributes); " - is this actual way to do this ?

No it isn't (but to my knowledge, it isn't exactly wrong either).

There used to be a function named EVP_PKEY_get0_RSA (e.g. : "const RSA *EVP_PKEY_get0_RSA(const EVP_PKEY *pkey);"  ) but that seems to be deprecated.

My google-foo seems off today (seem to be getting normal for me these days  :'( ) because I failed to find an answer that is better suited... so in that regards your solution is as good as any ?

actually all google and GPT solutions was like " rsa := PEM_read_bio_PrivateKey(bio, nil, nil, nil); " and all of them not work till find " pkey^.attributes " by chance 
its working now and its ok for me . but are you know updated openssl or any other crypto library to do this ? - synapse openssl3 was little bit Confusing for me . didnt have decrypt rsa function  at all and lockbox3 had its own formats and not workd for my keys .
and this c example did not even use " EVP_PKEY_get0_RSA "
https://hayageek.com/rsa-encryption-decryption-openssl-c/

[TRon]

Call it a coincidence but as luck would have it I was just reading that example while you posted your reply   

The problem with my google-foo is that all kinds of examples turn up either using the command-line or using deprecated functionality. The example you point to uses PEM_read_bio_RSAPrivateKey explicitly (and not PEM_read_bio_PrivateKey) which might account for the difference. How to properly use PEM_read_bio_PrivateKey and then obtain the rsa key is unclear to me, or it must be that when you provide the PPEVP_PKEY argument that it automatically returns the correct pointer to the rsa key ?

[victor11109]

Call it a coincidence but as luck would have it I was just reading that example while you posted your reply   

The problem with my google-foo is that all kinds of examples turn up either using the command-line or using deprecated functionality. The example you point to uses PEM_read_bio_RSAPrivateKey explicitly (and not PEM_read_bio_PrivateKey) which might account for the difference. How to properly use PEM_read_bio_PrivateKey and then obtain the rsa key is unclear to me, or it must be that when you provide the PPEVP_PKEY argument that it automatically returns the correct pointer to the rsa key ?

yes it seems to PPEVP_PKEY argument must automatically returns the correct pointer to the rsa key but it didnt.
the PPEVP_PKEY is record of

Code: Pascal  [Select][+][-]

1.   EVP_PKEY = record
2.     ktype: integer;
3.     save_type: integer;
4.     references: integer;
5.     pkey: EVP_PKEY_PKEY;
6.     save_parameters: integer;
7.     attributes: PSTACK_OFX509;
8.   end;      
9.  

and i find function " EvpPkeyAssign(pkey: PEVP_PKEY; _type: cInt; key: Prsa): cInt; " . are this related to problem ?
some ai code generators suggested  rsa := pkey^.pkey.rsa;  but its not work . this shoud be the actual way not ?