Use SHA256 by default in command line compilers

[tmat]

Customer scenario

The C# and VB command line compilers and build tasks use SHA1 by default for calculating hashes of source files stored in PDBs. It has already been possible to explicitly request SHA256 algorithm by specifying /checksumalgorithm:SHA256 on command line or setting ChecksumAlgorithm property in project file. This change makes SHA256 the default since SHA1 is no longer an acceptable crypto hash algorithm.

Bugs this fixes

Workarounds, if any

Set the algorithm explicitly.

Risk

Small.

Performance impact

Small.

I measured build of Microsoft.CodeAnalysis.dll in several configurations. The difference in compilation time between SHA1 and SHA256 is not measurable in end-to-end scenario. The size difference is 1% for Portable PDBs and none in Windows PDBs (due to section alignment).

Time (s)

	Portable PDB	Windows PDB
SHA1	3.6032	3.7272
SHA256	3.6030	3.7356
	99.99%	100.23%

PDB size (B)

	Portable PDB	Windows PDB
SHA1	953,792	6,641,152
SHA256	960,884	6,641,152
	101%	100%

Method:

1..100 | % {(Measure-Command { &csc /noconfig @CodeAnalysis.rsp args }).TotalSeconds} | Measure-Object -Average

where args are:

/debug:portable /checksumalgorithm:sha1
/debug:portable /checksumalgorithm:sha256
/debug:full /checksumalgorithm:sha1
/debug:full /checksumalgorithm:sha256

Is this a regression from a previous update?

Root cause analysis

How was the bug found?

Test documentation updated?

[tmat]

@jinujoseph @MattGertz Looks like the extra processing time of SHA256 is within the noise. The Portable PDB size increase of 1% is acceptable imo. The Windows PDB did not grow since it contains a lot of padding and alignment that was consumed by the larger hashes.

[MattGertz]

Groovy. @jac009 any concerns? This is in reference to the meeting we had on this transition last week.

[jac009]

@MattGertz Very torn on this. Would really like to understand what level of testing for teams that rely on PDBs (debuggers, profilers, Watson etc.) has been done.

[tmat]

@jac009 I'll get that info from the respective teams. The VS debugger has supported SHA256 since one of the Dev14 updates, VS Code and VS Mac Core CLR debugger since day one.

[tmat]

Before switching to SHA256 by default in the compilers we will first use the explicit switch in all our repositories to flush out any potential issues it might cause.

RepoToolset repos:

• http://github.com/dotnet/project-system
• http://github.com/dotnet/project-system-tools
• http://github.com/dotnet/interactive-window
• http://github.com/dotnet/symreader
• http://github.com/dotnet/symreader-portable
• http://github.com/dotnet/symreader-converter
• http://github.com/dotnet/symstore
• http://github.com/dotnet/metadata-tools
• http://github.com/dotnet/roslyn-analyzers
• http://github.com/dotnet/roslyn-debug (private)
• http://github.com/dotnet/roslyn-sdk (private)
• http://github.com/dotnet/roslyn-tools
• http://github.com/dotnet/dotnet-cli-archiver
• http://github.com/dotnet/clicommandlineparser
• http://github.com/dotnet/cli-migrate
• http://github.com/dotnet/sdk
• http://github.com/dotnet/xliff-tasks
• http://github.com/Microsoft/msbuild

Other repos:

• ASP.NET (Use SHA256 in PDBs aspnet/BuildTools#587)
• https://github.com/Microsoft/ApplicationInsights-dotnet (Use SHA256 for checksum algorithm microsoft/ApplicationInsights-dotnet#709)
• corefx
• coreclr
• corert
• .NET Native
• common
• javascriptservices
• netcorecli-fsc
• newtonsoft-json
• http://github.com/roslyn
• standard
• nuget-client
• dotnet/templating
• websdk
• core-setup
• https://github.com/Microsoft/visualfsharp (Add support for configurable hashing for source checksums fsharp#1223)
• DevDiv