AWS Cryptography Services - AWS Cryptographic Services

AWS cryptography services AWScryptographic services and tools guideCryptography concepts You can ask AWS Key Management Service (p. 10) (AWS KMS) to generate a data key. It returnsa plaintext key and a copy of that key that is encrypted under the customer master keys that youspecify.decryptionThe process of turning ciphertext (p. 3) back into plaintext (p. 6). Decryption algorithmstypically require an encryption key and can require other inputs, such as initialization vectors (IVs)and additional authenticated data (AAD) (p. 2).encryptionThe process of converting plaintext (p. 6) readable data to an unreadable form, known asciphertext (p. 3), to protect it. The formula used to encrypt the data, known as an encryptionalgorithm (p. 4), must be almost impossible (using current and anticipated technology) toreverse without knowledge of the inputs to the algorithm. These inputs can include an encryptionkey and other random and determined data.All of the cryptographic services and tools (p. 9) that AWS supports provide methods for you toencrypt and decrypt your data. Other AWS services automatically and transparently encrypt the datathat they store and manage for you.encryption algorithmA procedure or ordered set of instructions that specifies precisely how plaintext (p. 6) data istransformed into encrypted data or ciphertext (p. 3). The input to an encryption algorithmsincludes the plaintext data and a encryption key. The output includes the ciphertext.For example, AWS Key Management Service (p. 10) (AWS KMS) uses the Advanced EncryptionStandard (AES) symmetric (p. 2) algorithm in Galois/Counter Mode (GCM), known as AES-GCM.AWS CloudHSM (p. 9) supports keys for multiple encryption algorithms.encryption contextA type of additional authenticated data (AAD) (p. 2). It typically consists of nonsecret, arbitrary,name–value pairs. In most cases, you can provide an encryption context when you encrypt data. Thesame encryption context must be provided to decrypt the data. The encryption context is usuallyoptional but recommended.The term encryption context has different meanings in various AWS services and tools. This can beconfusing, so be sure to understand how your tool or service interprets this term.The following tools and services support an encryption context. In AWS Key Management Service (p. 10) (AWS KMS), an encryption context is a collection ofnonsecret name–value pairs. When you provide an encryption context to an encryption (p. 4)operation, AWS KMS binds it cryptographically to the ciphertext (p. 3). To decrypt the data,you must provide an exact, case-sensitive match for the encryption context.AWS KMS includes the encryption context in AWS CloudTrail logs of cryptographic operations. Assuch, you can use a well-designed encryption context to help you track and audit the use of yourencryption keys for particular projects or types of data.AWS KMS also lets you use all or part of the encryption context as the condition for a permissionin a policy or grant. For example, you can allow a user to use a master key to decrypt data onlywhen the encryption context includes a particular value.For details, see Encryption Context in the AWS Key Management Service Developer Guide. The AWS Encryption SDK (p. 11) also supports an optional encryption context in allcryptographic operations.However, you do not provide the encryption context to the decryption (p. 4) operation.Instead, when it encrypts data, the SDK saves the encryption context (in plaintext (p. 6)) along4

AWS cryptography services AWScryptographic services and tools guideCryptography conceptswith the ciphertext in the encrypted message that it returns. When you ask the SDK to decrypt theencrypted message, the SDK uses the encryption context that it saved.You can still use the encryption context to provide an additional verification of your data. Whenyou decrypt data, you can get and examine the encryption context and return the decrypted dataonly after verifying that the encryption context has the expected value. The DynamoDB Encryption Client (p. 12) uses encryption context to mean something differentfrom its use in AWS KMS or the AWS Encryption SDK. The DynamoDB encryption context isa collection of information about the table and table item that you pass to a cryptographicmaterials provider (CMP). It is not related to AAD.envelope encryptionA strategy for protecting the encryption keys that you use to encrypt your data. First, you encryptplaintext (p. 6) data with a data key (p. 3). Then, to protect the data key, you encrypt itunder another key, known as a key encryption key (p. 6).Encrypting the data key is more efficient than reencrypting the data under the new key because it isquicker and produces a much smaller ciphertext (p. 3).You can even encrypt the data encryption key under another encryption key and encrypt thatencryption key under still another encryption key. But, eventually, one key must remain in plaintextso you can decrypt the keys and your data. This top-level plaintext key encryption key is known asthe master key (p. 6), as shown in the following diagram.5

AWS cryptography services AWScryptographic services and tools guideCryptography conceptsSeveral AWS cryptographic tools and services (p. 9) support envelope encryption. AWS KeyManagement Service (p. 10) (AWS KMS) protects the master key that must remain in plaintext. Itsupplies master keys that never leave the service unencrypted. AWS KMS supports operations thatgenerate data keys that are encrypted under your master key. You can use the data keys to encryptyour data outside of AWS KMS.The AWS Encryption SDK (p. 11) automatically encrypts your data with a data key that isencrypted by a master key that you specify. The DynamoDB Encryption Client (p. 12) supportsmany encryption (p. 4) strategies, including envelope encryption with an AWS KMS customermaster key or with keys that you provide.hardware security module (HSM)A computing device that performs cryptographic operations and provides secure storage forcryptographic keys. Many HSMs have features that make them resistant to tampering or providereliable tamper detection.AWS CloudHSM (p. 9) lets you create, manage, and control your own HSMs in the cloud. AWSKey Management Service (p. 10) (AWS KMS) generates and protects the customer master keys(CMKs) that it provides in FIPS 140-2 validated HSMs that it manages for you. AWS KMS also letsyou create your CMKs in a custom key store backed by an AWS CloudHSM cluster that you own andmanage.key encryption keyIn envelope encryption (p. 5), a key encryption key is an encryption key that is used to encrypt adata key (p. 3) or another key encryption key. To protect the key encryption key, it is encryptedby using a master key (p. 6).The term key encryption key refers to how the key is used, not how it is constructed. Like allencryption keys, a key encryption key is typically implemented as a byte array that meets therequirements of the encryption algorithm (p. 4) that uses it.Several AWS services provide key encryption keys. The HSMs in a AWS CloudHSM (p. 9) cluster generate encryption keys that can be used as datakeys, key encryption keys, or master keys. You can ask AWS Key Management Service (p. 10) (AWS KMS) to generate a data key, then usethat key as a key encryption key outside of AWS KMS.master keyIn envelope encryption (p. 5), a master key is an encryption key that is used to encrypt otherencryption keys, such as data keys (p. 3) and key encryption keys (p. 6). Unlike data keys andkey encryption keys, master keys must be kept in plaintext (p. 6) so they can be used to decryptthe keys that they encrypted.The term master key usually refers to how the key is used, not how it is constructed. Like allencryption keys, a master key is typically implemented as a byte array that meets the requirementsof the encryption algorithm (p. 4) that uses it.AWS Key Management Service (p. 10) (AWS KMS) generates and protect master keys. Its customermaster keys (CMKs) are created, managed, used, and deleted entirely within AWS KMS.Several AWS services provide master keys. The HSMs in a AWS CloudHSM (p. 9) cluster generate encryption keys that can be used as datakeys, key encryption keys, or master keys. AWS Key Management Service (p. 10) (AWS KMS) generates and protects master keys. Itscustomer master keys (CMKs) are created, managed, used, and deleted entirely within AWS KMS.plaintextInformation or data in an unencrypted, unprotected, or human-readable form.6

AWS cryptography services AWScryptographic services and tools guideCryptographic algorithmsSee also: ciphertext (p. 3).private keyOne of two keys, along with public keys (p. 7), used to protect data in an asymmetricencryption (p. 2) scheme. Public and private keys are algorithmically generated in tandem: thepublic key is distributed to multiple trusted entities, and one of its paired private keys is distributedto a single entity. This way, a message can be authenticated because the public key signature provesthat a trusted entity encrypted and sent it. The message contents can also be secured so that only aprivate key holder can decrypt it.public keyOne of two keys, along with private keys (p. 7), used to protect data in an asymmetricencryption (p. 2) scheme. Public and private keys are algorithmically generated in tandem: thepublic key is distributed to multiple trusted entities, and one of its paired private keys is distributedto a single entity. This way, a message can be authenticated because the public key signature provesthat a trusted entity encrypted and sent it. The message contents can also be secured so that only aprivate key holder can decrypt it.stream cipherAn algorithm that operates one bit of a data at a time rather than encrypting one block of data at atime as in block ciphers (p. 3).Cryptographic algorithmsAn encryption algorithm is a formula or procedure that converts a plaintext message into an encryptedciphertext. Modern algorithms use advanced mathematics and one or more encryption keys to makeit relatively easy to encrypt a message but virtually impossible to decrypt it without knowing thekeys. Algorithms generally require a source of randomness. They may also involve multiple layers ofencryption, repeated permutation, and insertion of sequential one-time values to prevent attacks.AWS cryptography services rely on secure, open-source encryption algorithms that are vetted by publicstandards bodies and academic research. Some AWS tools and services enforce the use of a specificalgorithm, while others offer multiple algorithms and key sizes but recommend a default choice.This section describes some of the algorithms that AWS tools and services support. They fall into twocategories, symmetric and asymmetric, based on how their keys function.Topics Symmetric algorithms (p. 7) Asymmetric algorithms (p. 9)Symmetric algorithmsAWS cryptographic tools and services support two widely used symmetric algorithms. AES – Advanced Encryption Standard (AES) with 128-, 192-, or 256-bit keys. AES is often combinedwith Galois/Counter Mode (GCM) and known as AES-GCM. Triple DES – Triple DES (3DES) uses three 56-bit keys. The scheme works on a block of data by splittingit in two and iteratively applying arbitrary round functions derived from an initial function. Triple DESuses 48 rounds to encrypt a block of data.For instance, AWS Key Management Service uses the Advanced Encryption Standard (AES) algorithm inGalois/Counter Mode (GCM) with 256-bit secret keys.7

AWS cryptography services AWScryptographic services and tools guideCryptographic algorithmsAn encryption scheme is called symmetric if it uses the same key to both encrypt and decrypt a message.Technically, the encryption key e and decryption key d don't have to be exactly the same. All that'srequired is that it's computationally trivial to determine d when you know e and e when you know d.However, in most practical symmetric encryption schemes, e and d are the same.NoteSymmetric encryption is also called shared key, shared secret, and secret key encryption. It isnot called private key encryption. Convention reserves the term private key for asymmetriccryptography, which centers around the idea of a private key and a corresponding (but different)public key.Symmetric key encryption requires that all intended message recipients have access to the shared key.Therefore, a secure communication channel must be established among the participants so that the keycan be transmitted to each along with the ciphertext. This presents practical problems and limits the useof direct symmetric key exchange.The following illustrations show how encryption and decryption work with symmetric keys andalgorithms. In the first illustration, a symmetric key and algorithm are used to convert a plaintextmessage into ciphertext.The following illustration shows the same secret key and symmetric algorithm being used to turnciphertext back into plaintext.Symmetric key ciphers may be either block ciphers or stream ciphers. A block cipher divides the plaintextmessaged into fixed-length strings called blocks and encrypts one block at a time. Block ciphers aretypically considered to be more powerful and practical primitives than stream ciphers, but they'realso slower. Streamciphers encrypt each unit of plaintext (such as a byte), one unit at a time, with acorresponding unit from a random key stream. The result is a single unit of ciphertext.Both AES and 3DES are block ciphers.8

AWS cryptography services AWScryptographic services and tools guideCryptographic services and toolsAsymmetric algorithmsAWS services typically support RSA and Elliptic Curve Cryptography (ECC) asymmetric algorithms.These algorithms are useful for authentication and for establishing secure communication channelswhen it is inconvenient to share a symmetric key in advance. For example, Amazon CloudFront supportsa long list of assymmetric ciphers used by the SSL/TLS protocols to enable encrypted connections overthe web.An encryption scheme is called asymmetric if it uses one key — the public key — to encrypt and adifferent, but mathematically related, key — the private key — to decrypt. It must be computationallyinfeasible to determine the private key if the only thing one knows is the public key. Therefore, the publickey can be distributed publicly while the private key is kept secret and secure. Together the keys arereferred to as a key pair.Another more common name for asymmetric encryption is public-key cryptography. Public-keycryptography is typically based on mathematical problems that are relatively easy to perform but cannotbe easily reversed. These include factoring a large integer back into its component prime numbersand solving the elliptic curve discrete logarithm function. The RSA algorithm is based on the practicaldifficulty of factoring the product of two large prime numbers. Elliptic-curve cryptography is based onthe difficulty of finding the discrete logarithm of a random point on an elliptic curve given a publiclyknown point.AWS cryptographic services and toolsAWS's cryptographic services utilize a wide range of encryption and storage technologies that can assurethe integrity of your data at rest or in transit. AWS offers several tools for cryptographic operations: AWS CloudHSM (p. 9) provides hardware security modules (HSMs) (p. 6) that can securelystore a variety of cryptographic keys, including master keys (p. 6) and data keys (p. 3). AWS Key Management Service (KMS) (p. 10) provides tools for generating master keys (p. 6)and other data keys (p. 3). AWS KMS also interacts with many other AWS services to encrypt theirservice-specific data. AWS Encryption SDK (p. 11) provides a client-side encryption library for implementing encryptionand decryption operations on all types of data. Amazon DynamoDB Encryption Client (p. 12) provides a client-side encryption library forencrypting data tables before sending them to a database service, such as Amazon DynamoDB. AWS Secrets Manager (p. 12) provides encryption and rotation of encrypted secrets used withAWS-supported databases.Many AWS services rely on these cryptographic services during data transfer or storage. For a list of suchservices and an overview of how they use cryptographic practices, see Other AWS Services (p. 13).AWS cryptographic services comply with a wide range of cryptographic security standards, making iteasy for you to protect your data without worrying about governmental or professional regulations. Fora full list of AWS data security standard compliances, see AWS Compliance Programs.AWS CloudHSMAWS CloudHSM is a cryptographic service for creating and maintaining hardware security modules(HSMs) in your AWS environment. HSMs are computing devices that process cryptographic operationsand provide secure storage for cryptographic keys. You can use AWS CloudHSM to offload SSL/TLSprocessing for web servers, protect private keys linked to an issuing certificate authority (CA), or enableTransparent Data Encryption (TDE) for Oracle databases.9

AWS cryptography services AWScryptographic services and tools guideAWS KMSWhen you use an HSM from AWS CloudHSM, you can perform a variety of cryptographic tasks: Generate, store, import, export, and manage cryptographic keys, including symmetric keys andasymmetric key pairs. Use symmetric and asymmetric algorithms to encrypt and decrypt data. Use cryptographic hash functions to compute message digests and hash-based messageauthentication codes (HMACs). Cryptographically sign data (including code signing) and verify signatures. Generate cryptographically secure random data.AWS CloudHSM organizes HSMs in clusters, which are automatically synchronized collections of HSMswithin a given Availability Zone (AZ). By adding more HSMs to a cluster and distributing clusters acrossAZs, you can load balance the cryptographic operations being performed

Cryptography uses a number of tools, typically called primitives, to provide information security. A primitive is a cryptographic algorithm. This includes encryption algorithms, digital signature algorithms, hashes, and other functions.