Extract public key modulus java. 1 As per https://crypto. RSACrack is a toolbox for deriving private key files from a given public key file, modulus or base64 encoded key. I was able to get PrivateKeyInfo object how can i get the modulus value from this? I have this public key that is generated from Delphi 10. This guide will walk you through how to extract an RSA public key from a private key using Java’s cryptographic APIs, validate the extracted key, and troubleshoot common pitfalls. I guess I made some mistake in the code, but it is weird that I get everything I want, except for the public key. The conversion works correct for the public key but fails to private key when comparing the encoded private keys. I currently Have the following: private void createPublicKey() throws NoSuchAlgorithmExc An RSA key is made up of a modulus and an exponent so I would hazard a guess that the exponent length would be the key length - modulus length but I am by no means certain. Certyficate is PEM . Check if it is a key entry (including private keys). Is there any way i can extract modulus and exponent from the public key. This tool is for for RSA encryption, decryption and to generate RSA key pairs online. Dear sir I have modulus and exp of the public key, how can i combine them to ge the complete public key, in the host app. pem command. How do I properly get to the modulus value as Base64urlUInt? Example GatewayScript code snippets to help the creation of a gatewayscript policy. KeyPairGenerator kpg = KeyPairGenerator. I've seen a private key is composed of : modulus publicExponent privateExponent prime1 prime2 exponent1 exponent2 coefficient I've been able to retrieve : modulus prime1 Hi friends, I'm extracting the public key from the X. For a der file, note also that the public key in DER format (which is a way of expressing X. pem -pubout -out public. The public key consists of $ (n, e)$, the modulus (product of two large primes), and the encryption exponent. I need use openssl to extract this public key. How do I properly get to the modulus value as Base64urlUInt? Factorizing a well-chosen 2048 bit modulus is infeasible at the current time. BigInteger following the RSA key generation algorithm to generate a correct keys. RSAPublicKeySpec public RSAPublicKeySpec(BigInteger modulus, BigInteger publicExponent, AlgorithmParameterSpec params) Creates a new RSAPublicKeySpec with additional key parameters. stackexchange. 2 TurboPower LockBox 2 module: MIGIAoGBALtEMVXxHBWzBx/AzO/aOHrYEQZB3VlqYBvqX/SHES7ehERXaCbUO5aEwyZcDrdh2dMTy I am kinda new to cryptography, and a requirement needs me to "Create or retrieve user’s RSA-OAEP key. getEncoded ("hex"); Dec 10, 2025 · This guide will walk you through how to extract an RSA public key from a private key using Java’s cryptographic APIs, validate the extracted key, and troubleshoot common pitfalls. Closed 6 years ago. I have public certificate with 2048 bit RSA public key for encrypt data. getPublicKey ());" to extract the publick key from the certificate. pem So, here my question: Is there an easy way to get key size, modulus, public exponent, private exponent from a PEM file using fundamental5 library ? FYI: I'm using fundamentals v5. I am doing a hacking challenge but I don't manage to know how to decrypt the private key from the public key and the given private key "prime1" parameter. 2 TurboPower LockBox 2 module: MIGIAoGBALtEMVXxHBWzBx/AzO/aOHrYEQZB3VlqYBvqX/SHES7ehERXaCbUO5aEwyZcDrdh2dMTy Subject Public Key Algorithm: Identifies the algorithm used to generate the public key (e. Issuer/Subject Unique Identifier: These fields are optional and might only appear if the certificate version is 2 or 3. i'm using bouncy castle api . Parameters: modulus - the modulus publicExponent - the public exponent params - the parameters associated with this key, may be null Since: 8 Method Detail getModulus public BigInteger getModulus() To extract public key from the private key file into separate public key file you use your openssl rsa -in private. out. Private key consist of various components such as modulus, public exponent, private exponent, coefficient, etc. I use comm Tool to decrypt/encrypt with RSA cipher. Unlike symmetric keys, RSA private keys (in most standard formats) contain the mathematical components required to derive the public key. However, many private key storage formats actually contain the public modulus n alongside the other components, so you can just do a direct extraction of the values. println("base64 modulus = " + modulus); // To convert to hex: CkBinData binDat = new CkBinData (); binDat. pem but I don't know how (using openssl) to create a public key having just it's modulus and exponent. I'm trying to duplicate the functionality in C# without success. Unless it is known that this modulus was selected to be easy to factor (say, in a CTF challenge), you are quite unlikely to succeed. Both public and private keys can be generated for free. From pem file, Using the below command in terminal: openssl x50 Nov 21, 2025 · This blog will guide you through converting RSA public key components (modulus and exponent) to PEM format using two approaches: 1. I am trying to get the modulus value of a private key using bouncy castle library. . verify() invocation returns false because the public key specified within the JWK in the request does not match the key used to sign the request. Additionally, let’s use try-with-resources so we don’t have to worry about closing the InputStream manually. 4 From the discussion with @Topaco in the comments: The code in the question does successfully construct the RSA public key from the modulus n and the exponent e. This article explains how to reconstruct an RSA public key using a given exponent and modulus. 509 objects as a sequence of bytes) includes more than just the modulus, but also the exponent (usually short) and the algorithm identifier The specs say this: 6. This tutorial shows how to extract public key from private key using OpenSSL. 4 and Delphi 7. When I am trying to extract modulus and exponent components from public key which is in . The pubkey is just null. Retrieve and print the private key in PKCS8 format. It may talk to a daemon to access the underlying hardware, or it may be talking directly. pem file, using below command: openssl rsa -inform der -pubin -text < pubkey. Are there any examples as to how to get this information using BouncyCastle and Java? Note The PKCS #11 library is running within your process, using your memory, etc. By Alexey Samoshkin When it comes to security-related tasks, like generating keys, CSRs, certificates, calculating digests, debugging TLS connections and other tasks related to PKI and HTTPS, you’d most likely end up using the OpenSSL tool. I have this public key that is generated from Delphi 10. AppendEncoded (modulus, "base64"); String hexModulus = binDat. Extract modulus and exponent from public key. Conclusion Listing private keys from a keystore can be done using both command line tools and Java programs. From pem file, Using the below command in terminal: openssl x50 I wanted to ask how to retrieve the actual values of the private and public keys from the KeyPair object because i need to export them and save in a database. It is represented as a Base64urlUInt-encoded value. RSA is an asymmetric algorithm for public key cryptography created by Ron Rivest, Adi Shamir and Len Adleman. Learn how to retrieve the exponent and modulus from an RSA public key stored in a PFX or PEM file using Java. I've tried to use bouncycastle to extract the relevant Modulus and Exponent from the ASN. I want to separate the modulus $n$ and exponent $e$. From a Base64 public key, it parses the modulus and exponent, generates a public key and then encrypts some card data. You won't find a modulus if your private key or your certificate is signed with ECC (Elliptic Curve Cryptography)! Run following commands and compare the output. I want to use RSA public key encryption. pem contains a RSA PUBLIC KEY) openssl rsa -pubin -inform PEM -text -noout < public. 1. GitHub Gist: instantly share code, notes, and snippets. Any suggestions are greatl I'm currently doing RSA encryption on Java and I have to use private and public modulus for the encryption. getChildContent ("Modulus"); System. 3. Are there any examples as to how to get this information using BouncyCastle and Java? The only solution I could find is to print the key to a buffer via EVP_PKEY_print_public (), parse the result to extract the modulus into a giant hex string, and then BN_hex2bn () that back into a BIGNUM. 509 certificate . , RSA, DSA, or Diffie-Hellman). it is giving me the modulus and the exponent given below : I'm trying to generate a pair of keys from modulus,public exponent and private exponent to cipher a string and then decipher it, but the deciphered output is different from the input. 1 file, and using OpenSSL to generate the public key in PEM format. What is the best way to store or retrieve private and public keys? Is XML a good idea here? How to get the keys? RSAParameters privateKey = RSA. If you are looking for a way to create a public key (PEM or SSH format), starting from the modulus and the exponent and without any piece of code, then you reached the right place! I know I can use openssl rsautl -verify -in sig -inkey key. 1a:82:cc:93:8b:48:31:38:43:24:bd:04:01:fa:12:16:3a:50: 57:0e:68:4d But I don't get the public key modulus and the other necessary stuff when I'm using Bouncy Castle. However, the Signature. API Note: This method is defined in Java SE 8 Maintenance Release 3. I want to convert - RSA Public Key modulus: I am using "out. cer file, and extracted key should be PEM too. 0. Step-by-step guide and code snippet included. println ("Public key: "+x509certificate. math. I couldn't find any information on how to grab modulus and exp from a key generated with ssh-keygen so I tried to manually extract it with some help from this post to get: Do not distribute anything other than the Modulus and Public Exponent, which are found in both the Private and Public key. "n" (Modulus) Parameter The "n" (modulus) parameter contains the modulus value for the RSA public key. I want to extract information about RSA Public Key from the pfx file using java. Environment variables set on your process can be used to configure the behaviour of the library, check the documentation for your device. There should be one public/private key pair for each user for a device" and send it to the The only thing missing from a raw private key is e, but this value is usually selected as 65537, and if not you can still compute e from d and λ (n). When public keys are distributed, they are usually done by giving out a signed X509 certificate, which contains the public key, identification information linking that key to an entity, and a signature from a trusted authority. BTW, I haven't found a possibility to programmatically extract the modulus and public exponent needed for the constructor of RSAPublicKeySpec. Given a RSA private key modulus and private exponent only, which is all I have (and also enough for all crypto related operations), can I get the associated public key modulus and public exponent? Also, can I get the encoded form of the private key with only those two parameters? 1 As per https://crypto. g. Any suggestions are greatl Java RSA - Constructing public key using modulus string and public exponent string Asked 8 years, 7 months ago Modified 8 years, 7 months ago Viewed 859 times This article explains how to reconstruct an RSA public key using a given exponent and modulus. When you produce a public key this way, it is extracted from the private key file, not calculated. public class I've tried to use bouncycastle to extract the relevant Modulus and Exponent from the ASN. com/questions/18105/how-does-recovering-the-public-key-from-an-ecdsa-signature-work, I should be able to recover an ECDSA public key if I have a signature and the message it is signing. Learn how to retrieve the exponent and modulus from an RSA public key stored in a PFX or PEM file using Java. Parameters: modulus - the modulus publicExponent - the public exponent // We can get the base64 modulus like this: String modulus = xml. I have a pfx file and converted to x509 Pem file. At the time of writing it supports cracking RSA keys of 128, 256 bits in minutes. It is the most used in data exchange over the Internet. It outlines the process of converting these values to hexadecimal, creating an ASN. Is there a way to extract modulus and exponent of a private key using openssl? If there is a way, please let me know. Hi friends, I'm extracting the public key from the X. Subject Public Key: The subject's public key. OpenSSL i In resume you have to calculate the modulus, public exponent and private exponent with java. I'm trying to rebuild a RSA keypair from modulus & private/public exponents. Creates a new RSAPublicKeySpec with additional key parameters. 4. ExportPara You won't find a modulus if your private key or your certificate is signed with ECC (Elliptic Curve Cryptography)! Run following commands and compare the output. 1 buffer but it crashes with SigSegV when it tries to do the Modulus in the example below. These values are coming from the java card ?? i am getting these as follows: Get key size, modulus, public exponent, (public. pem The specs say this: 6. **Java Standard Libraries** (no external dependencies, with manual PEM encoding). So it's probably easier to just convert from PKCS#1 to PKCS#8 with openssl or similar programs Is there a way via an CLI tool or some kind of API to extract the PGP key ID from the PGP public key block? I found the hexa value of the key in the binary file, but I guess the position is based on the key kind/size. drdcaj, ffqpyq, kvkj, ylc3, 4itab, mbbo12, hd6ko, 1paidw, b6kil8, ymny1,