Hashed message is signed by a sender using what?

In this article This article discusses how message authentication codes (MACs), hashes, and signatures can be used in Universal Windows Platform (UWP) apps to detect message tampering. Message authentication codes (MACs) Encryption helps prevent an unauthorized individual from reading a message, but it does not prevent that individual from tampering with the message. An altered message, even if the alteration results in nothing but nonsense, can have real costs. A message authentication code (MAC) helps prevent message tampering. For example, consider the following scenario: • Bob and Alice share a secret key and agree on a MAC function to use. • Bob creates a message and inputs the message and the secret key into a MAC function to retrieve a MAC value. • Bob sends the [unencrypted] message and the MAC value to Alice over a network. • Alice uses the secret key and the message as input to the MAC function. She compares the generated MAC value to the MAC value sent by Bob. If they are the same, the message was not changed in transit. Note that Eve, a third party eavesdropping on the conversation between Bob and Alice, cannot effectively manipulate the message. Eve does not have access to the private key and cannot, therefore, create a MAC value which would make the tampered message appear legitimate to Alice. Creating a message authentication code ensures only that the original message was not altered and, by using a shared secret key, that the message hash was signed by som...

SOLUTION The correct option is 1 i.e., Hashed message. • The hashed messageis signed by a sender by using his private key. • Rather than encrypting the data itself, wecan create a one-way hash of the data and then use your private key to encrypt the hash. • The encrypted hash, along with other information like the hashing algorithm, is known as a digital signature • A hashed message authentication code (HMAC) is a message authentication code that makes use of a cryptographic key along with a hash function. • A private keyis a variable in cryptography that is used with an algorithm to encrypt and decrypt code • A public key is a large numerical value that is used to encrypt data.

In this article The following example hashes some data and signs that hash. In a second phase, the hash and its signature are verified. The hash is signed with the user's private key, and the signer's public key is exported so that the signature can be verified. This example illustrates the following tasks and CryptoAPI functions: • Acquiring a CSP using CryptAcquireContext. • Getting the user's AT_SIGNATURE key pair using CryptGetUserKey. • Creating a PUBLICKEYBLOB with the signer's public key to be used in the signature verification process using CryptExportKey. • Creating a hash object using CryptCreateHash. • Hashing the data using CryptHashData. • Signing the hash using CryptSignHash. • Destroying the original hash object using CryptDestroyHash. • Making the public key needed to verify the hash available using CryptImportKey. • Re-creating the hash object using CryptCreateHash and CryptHashData. • Verifying the signature on the hash using CryptVerifySignature. • Performing normal cleanup. //-------------------------------------------------------------------- // Copyright (C) Microsoft. All rights reserved. // Example of signing a hash and // verifying the hash signature. #pragma comment(lib, "crypt32.lib") #include #include #include #define MY_ENCODING_TYPE (PKCS_7_ASN_ENCODING | X509_ASN_ENCODING) void MyHandleError(char *s); void main(void) // End of MyHandleError  Â

I am trying to get a better grapple on how public/private keys work. I understand that a sender may add a digital signature to a document using his/her private key to essentially obtain a hash of the document, but what I do not understand is how the public key can be used to verify that signature. My understanding was that public keys encrypt, private keys decrypt... can anyone help me understand? I didn't want to add this as an answer and risk the ensuing flames but if you're use of the word "how" really means "how do I verify a signature" then one possibility is to download gpg4win. Once installed, you can right-click a file and verify it. It is a suite of products that integrate into the Windows shell. One such utility is Kleopatra that will look up certificates online to do the validation. Public keys aren't used to encrypt, they're used to sign. The terminology is important because if something is "encrypted", it means it's almost impossible for any person (who doesn't have the private key) to get back the original message. This obviously isn't the case if you sign something with a private key because anyone can get the public key and decrypt the ciphertext to get back the original message. Your understanding of "public keys encrypt, private keys decrypt" is correct... for data/message ENCRYPTION. For digital signatures, it is the reverse. With a digital signature, you are trying to prove that the document signed by you came from you. To do that, you need to use somet...

The As diagram shows, the message is first hashed, and the signature is then computed on the hash, rather than on the full message. Why hash the data before signing it? Why not sign the whole message? Of course, it'll save time if you sign just the hash value, but I've heard there are also security issues with directly signing the full message. If so, what are they? In addition to the performance problems Reordering If you have a message $m>N$ with $N$ being the RSA modulus, then you have to perform at least 2 RSA signatures as $m$ does not longer fit into $Z_N$. Let us assume that it requires $k$ such signatures and write the message $m=(m_1,\ldots,m_k)$ and the overall signature will be $\sigma=(\sigma_1,\ldots,\sigma_k)$, i.e., $k$ RSA signatures. Now without any additional measures, anyone getting to hold $(m,\sigma)$ can manipulate the message and adopt the signature by 1) swapping any pair of sub-message $m_i$, $1\leq i\leq k$ and corresponding sub-signature $\sigma_i$ or 2) dropping a sub-message and corresponding sub-signature. As an example for swapping lets say we have $m=(m_1,m_2,m_3)$ and thus $\sigma=(\sigma_1,\sigma_2,\sigma_3)$, i.e., 3 indepenendet RSA signatures for a message consisting of 3 blocks, then an adversary who gets $(m,\sigma)$ can simply swap, for instance to $m'=(m_2,m_3,m_1)$ and $\sigma'=(\sigma_2,\sigma_3,\sigma_1)$, which is a forgery, as it clearly is a valid signature. Existential forgery If you do not use a redundancy scheme for message...

Exam Question While sending a signed message, a sender • 1. sends message key using public key encryption using DES and hashed message using public key encryption • 2. sends message using public key encryption and hashed message using DES • 3. sends both message and hashed message using DES • 4. sends both message and hashed message using public key encryption Answer Answer 1. sends message key using public key encryption using DES and hashed message using public key encryption Practice set and Exam Quiz Yes! You can do Online MCQ practice of E-Commerce question set and give online exam quiz test for E-Commerce, so you can check your knowledge. You can get MCQ Study and Exam link from home page. Post navigation

Exam Question While sending a signed message, a sender • 1. sends message key using public key encryption using DES and hashed message using public key encryption • 2. sends message using public key encryption and hashed message using DES • 3. sends both message and hashed message using DES • 4. sends both message and hashed message using public key encryption Answer Answer 1. sends message key using public key encryption using DES and hashed message using public key encryption Practice set and Exam Quiz Yes! You can do Online MCQ practice of E-Commerce question set and give online exam quiz test for E-Commerce, so you can check your knowledge. You can get MCQ Study and Exam link from home page. Post navigation

SOLUTION The correct option is 1 i.e., Hashed message. • The hashed messageis signed by a sender by using his private key. • Rather than encrypting the data itself, wecan create a one-way hash of the data and then use your private key to encrypt the hash. • The encrypted hash, along with other information like the hashing algorithm, is known as a digital signature • A hashed message authentication code (HMAC) is a message authentication code that makes use of a cryptographic key along with a hash function. • A private keyis a variable in cryptography that is used with an algorithm to encrypt and decrypt code • A public key is a large numerical value that is used to encrypt data.

The As diagram shows, the message is first hashed, and the signature is then computed on the hash, rather than on the full message. Why hash the data before signing it? Why not sign the whole message? Of course, it'll save time if you sign just the hash value, but I've heard there are also security issues with directly signing the full message. If so, what are they? In addition to the performance problems Reordering If you have a message $m>N$ with $N$ being the RSA modulus, then you have to perform at least 2 RSA signatures as $m$ does not longer fit into $Z_N$. Let us assume that it requires $k$ such signatures and write the message $m=(m_1,\ldots,m_k)$ and the overall signature will be $\sigma=(\sigma_1,\ldots,\sigma_k)$, i.e., $k$ RSA signatures. Now without any additional measures, anyone getting to hold $(m,\sigma)$ can manipulate the message and adopt the signature by 1) swapping any pair of sub-message $m_i$, $1\leq i\leq k$ and corresponding sub-signature $\sigma_i$ or 2) dropping a sub-message and corresponding sub-signature. As an example for swapping lets say we have $m=(m_1,m_2,m_3)$ and thus $\sigma=(\sigma_1,\sigma_2,\sigma_3)$, i.e., 3 indepenendet RSA signatures for a message consisting of 3 blocks, then an adversary who gets $(m,\sigma)$ can simply swap, for instance to $m'=(m_2,m_3,m_1)$ and $\sigma'=(\sigma_2,\sigma_3,\sigma_1)$, which is a forgery, as it clearly is a valid signature. Existential forgery If you do not use a redundancy scheme for message...

I am trying to get a better grapple on how public/private keys work. I understand that a sender may add a digital signature to a document using his/her private key to essentially obtain a hash of the document, but what I do not understand is how the public key can be used to verify that signature. My understanding was that public keys encrypt, private keys decrypt... can anyone help me understand? I didn't want to add this as an answer and risk the ensuing flames but if you're use of the word "how" really means "how do I verify a signature" then one possibility is to download gpg4win. Once installed, you can right-click a file and verify it. It is a suite of products that integrate into the Windows shell. One such utility is Kleopatra that will look up certificates online to do the validation. Public keys aren't used to encrypt, they're used to sign. The terminology is important because if something is "encrypted", it means it's almost impossible for any person (who doesn't have the private key) to get back the original message. This obviously isn't the case if you sign something with a private key because anyone can get the public key and decrypt the ciphertext to get back the original message. Your understanding of "public keys encrypt, private keys decrypt" is correct... for data/message ENCRYPTION. For digital signatures, it is the reverse. With a digital signature, you are trying to prove that the document signed by you came from you. To do that, you need to use somet...