Extract public key modulus java. What is the best way to ...

Extract public key modulus java. 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. 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. getPublicKey ());" to extract the publick key from the certificate. 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. GitHub Gist: instantly share code, notes, and snippets. , RSA, DSA, or Diffie-Hellman). I want to use RSA public key encryption. The conversion works correct for the public key but fails to private key when comparing the encoded private keys. Creates a new RSAPublicKeySpec with additional key parameters. 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. This tutorial shows how to extract public key from private key using OpenSSL. pem command. pem but I don't know how (using openssl) to create a public key having just it's modulus and exponent. When I am trying to extract modulus and exponent components from public key which is in . I have a pfx file and converted to x509 Pem file. For a der file, note also that the public key in DER format (which is a way of expressing X. At the time of writing it supports cracking RSA keys of 128, 256 bits in minutes. 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. KeyPairGenerator kpg = KeyPairGenerator. It outlines the process of converting these values to hexadecimal, creating an ASN. I want to separate the modulus $n$ and exponent $e$. The pubkey is just null. I need use openssl to extract this public key. 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. 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. 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. 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. i'm using bouncy castle api . I use comm Tool to decrypt/encrypt with RSA cipher. Step-by-step guide and code snippet included. Conclusion Listing private keys from a keystore can be done using both command line tools and Java programs. println("base64 modulus = " + modulus); // To convert to hex: CkBinData binDat = new CkBinData (); binDat. This tool is for for RSA encryption, decryption and to generate RSA key pairs online. Issuer/Subject Unique Identifier: These fields are optional and might only appear if the certificate version is 2 or 3. 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. From a Base64 public key, it parses the modulus and exponent, generates a public key and then encrypts some card data. g. How do I properly get to the modulus value as Base64urlUInt? Factorizing a well-chosen 2048 bit modulus is infeasible at the current time. It is the most used in data exchange over the Internet. 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. Hi friends, I'm extracting the public key from the X. I guess I made some mistake in the code, but it is weird that I get everything I want, except for the public key. Both public and private keys can be generated for free. Subject Public Key: The subject's public key. println ("Public key: "+x509certificate. I'm trying to rebuild a RSA keypair from modulus &amp; private/public exponents. 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. Check if it is a key entry (including private keys). cer file, and extracted key should be PEM too. Is there a way to extract modulus and exponent of a private key using openssl? If there is a way, please let me know. 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. 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. 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. Learn how to retrieve the exponent and modulus from an RSA public key stored in a PFX or PEM file using Java. 2 TurboPower LockBox 2 module: MIGIAoGBALtEMVXxHBWzBx/AzO/aOHrYEQZB3VlqYBvqX/SHES7ehERXaCbUO5aEwyZcDrdh2dMTy Subject Public Key Algorithm: Identifies the algorithm used to generate the public key (e. Extract modulus and exponent from public key. stackexchange. RSAPublicKeySpec public RSAPublicKeySpec(BigInteger modulus, BigInteger publicExponent, AlgorithmParameterSpec params) Creates a new RSAPublicKeySpec with additional key parameters. "n" (Modulus) Parameter The "n" (modulus) parameter contains the modulus value for the RSA public key. 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). 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. 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. 4. 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. These values are coming from the java card ?? i am getting these as follows: Get key size, modulus, public exponent, (public. Any suggestions are greatl I'm currently doing RSA encryption on Java and I have to use private and public modulus for the encryption. out. However, the Signature. pem -pubout -out public. Private key consist of various components such as modulus, public exponent, private exponent, coefficient, etc. BTW, I haven't found a possibility to programmatically extract the modulus and public exponent needed for the constructor of RSAPublicKeySpec. **Java Standard Libraries** (no external dependencies, with manual PEM encoding). I want to convert - RSA Public Key modulus: I am using "out. How do I properly get to the modulus value as Base64urlUInt? Example GatewayScript code snippets to help the creation of a gatewayscript policy. 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. It may talk to a daemon to access the underlying hardware, or it may be talking directly. 4 and Delphi 7. 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 have this public key that is generated from Delphi 10. Parameters: modulus - the modulus publicExponent - the public exponent // We can get the base64 modulus like this: String modulus = xml. I want to extract information about RSA Public Key from the pfx file using java. Closed 6 years ago. 509 certificate . When you produce a public key this way, it is extracted from the private key file, not calculated. 1 file, and using OpenSSL to generate the public key in PEM format. . 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. 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. Environment variables set on your process can be used to configure the behaviour of the library, check the documentation for your device. Additionally, let’s use try-with-resources so we don’t have to worry about closing the InputStream manually. I've tried to use bouncycastle to extract the relevant Modulus and Exponent from the ASN. 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. API Note: This method is defined in Java SE 8 Maintenance Release 3. Certyficate is PEM . 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. BigInteger following the RSA key generation algorithm to generate a correct keys. Unlike symmetric keys, RSA private keys (in most standard formats) contain the mathematical components required to derive the public key. The public key consists of $ (n, e)$, the modulus (product of two large primes), and the encryption exponent. public class I've tried to use bouncycastle to extract the relevant Modulus and Exponent from the ASN. AppendEncoded (modulus, "base64"); String hexModulus = binDat. OpenSSL i In resume you have to calculate the modulus, public exponent and private exponent with java. 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. 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. Learn how to retrieve the exponent and modulus from an RSA public key stored in a PFX or PEM file using Java. 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. RSACrack is a toolbox for deriving private key files from a given public key file, modulus or base64 encoded key. 1 buffer but it crashes with SigSegV when it tries to do the Modulus in the example below. Is there any way i can extract modulus and exponent from the public key. I'm trying to duplicate the functionality in C# without success. 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. I have public certificate with 2048 bit RSA public key for encrypt data. 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. 1. 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. 3. getChildContent ("Modulus"); System. 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. This article explains how to reconstruct an RSA public key using a given exponent and modulus. 1 As per https://crypto. pem contains a RSA PUBLIC KEY) openssl rsa -pubin -inform PEM -text -noout < public. 0. math. Retrieve and print the private key in PKCS8 format. pem The specs say this: 6. 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. pem file, using below command: openssl rsa -inform der -pubin -text < pubkey. 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. I am trying to get the modulus value of a private key using bouncy castle library. 8ompaq, sbbf, g45m5, 1xyj, w1zmqp, 5ubus, hvcd, pgf6x, ebxtj, pbfmb,